Abstract

Psychopathy and serial killing are frequently intertwined concepts that have intrigued and horrified society and psychologists alike. While not all psychopaths become serial killers, certain psychological, environmental and situational factors contribute to this outcome. This article explores the interconnected factors that drive some psychopaths to commit repeated acts of murder, such as the role of parenting, attachment and genetics that lead to progressive acts of violence. By reviewing case studies, meta-analyses and empirical studies, this article aims to display the complexity of both nature and nurture in the minds of serial killers. Understanding these factors is not only helpful for psychological insights, but also for developing strategies to detect, intervene and prevent future tragedies. Ultimately, this article highlights the importance of addressing both innate traits of psychopathy and external factors that may contribute to destructive outcomes of this personality disorder.

1. Introduction

The American Psychological Association (APA) defines anti-social personality disorder (ASPD) as the presence of a consistent need to disregard and violate the rights of others (APA Dictionary of Psychology, n.d.). Individuals with ASPD frequently present with psychopathic traits including a lack of empathy, poor impulse control and manipulative behaviour (Frazier et al., 2019). 

The largest difference between sociopaths and psychopaths is that the former hold the capability for empathy that the latter do not (Clark et al., 2017). Furthermore, sociopaths have no regard for social norms and are prone to impulsive and erratic behaviour, while psychopaths maintain superficial charm and stay calm under pressure (Spytska, 2024). While not all psychopaths become homicidal, some exhibit behaviours making them known as serial killers (Fox & DeLisi, 2018). By definition, serial killers are those who kill at least three people over a period of time that includes “cooling off” (Miller, 2013). Psychopathic serial killers are typically motivated by thrills from manipulating and exploiting others, yet can maintain their daily lives along with their criminality (Miller, 2013).

Those who are diagnosed with psychopathy alone or have psychopathic traits do not immediately turn to violence, so this research is crucial to clarify the additional factors that cause one’s mind to hold the obsession with taking someone’s life. It is also beneficial to be able to establish clearly the main factors and influences that separate a non-violent psychopath from a violent one. This pursuit of knowledge also paves the way for change, as the answer could result in significantly improved treatment and solutions targeted towards those who develop psychopathic traits. This creates the opportunity to intervene earlier regarding those who show signs of violence, before their behaviour has a chance to escalate.

The literature review will explore the origin of psychopaths that become serial killers. Starting with the cause of psychopathy, since it can look different on different individuals, it is crucial to understand the different types of attachment, the influence of one’s environment and the potential role genetics can play in creating a psychopath. This paper will then investigate the types of victims, method of killing and “signature styles” of serial killers that originate from their desire to fulfill their emotional needs (Bohn, 2015). Understanding what triggers psychopathic serial killers to start offending is crucial for preventing future dangers to society. This research paper seeks to answer the question: why do some psychopaths become serial killers?

2. Literature Review

2.1 Early Child Development: Violent Psychopaths

Psychopathy is a complex personality that directly relates to specific traits such as reduced empathy, lack of remorse, shallow emotional responses, manipulation and persistent anti-social behaviour (Hare, 2009). Even though psychopathy is generally evaluated in adulthood, research shows that behaviours start in childhood, first as oppositional defiant disorder (ODD) until the age of eight, after which point if behaviours become more harmful and aggressive, it is diagnosed as conduct disorder (CD) through the age of seventeen. Psychopathy is thought to develop through an interaction between genetic vulnerability, brain development, temperament, attachment, childhood adversity, parenting and learnt behaviors from  social environments (Hare & Neumann, 2009). 

Childhood developmental traits present in a subgroup of anti-social children who may have a natural tendency to become psychopaths are lack of guilt, shallow empathy and low concern for consequences. Callous-unemotional (CU) traits have been identified as potential early indicators of pathways linked to psychopathic traits (Frick & Ray, 2015). CU traits can be identified as early as age three, including reduced fear response, low empathy and reduced attention to caregivers’ emotional cues (Waller & Hyde, 2017). Researchers suggest that there is a direct link between early CU markers and later violent behaviour, as CU traits in first-time adolescent arrestees increased the chance of gun violence after a four-year follow-up (Walker, Frick & Robertson, 2020). Children with CU traits are more likely to commit goal-oriented violence rather than impulsive violence (Raine et al., 2006), although at-risk children display impulsivity, much like those with attention deficit hyperactivity disorder (ADHD). 

According to Waller and Hyde (2016), early indicators of psychopathy, such as low empathy and lack of remorse and/or guilt, indicate that the child has little to no concern for another person’s feelings and a disregard for the emotional impact of their actions when hurting somebody or breaking a rule. Unconcern about performance is another key marker, indicating that the child is not affected when failing a test or not meeting expectations. They typically have low sensitivity to distress, meaning the child may not respond to fear, sadness, crying or feel another’ s pain. The child may use others to achieve the outcome they want, treating them as instruments. Repetition is another CU marker, as one single occurrence of a CU trait does not instantly mean that the person is a psychopath, but consistent recurrences of these CU markers may indicate psychopathy (Waller & Hyde, 2016).

2.2 Environmental Influences

A meta-analysis of ten studies involving 5,731 young children shows that these traits are linked to serious behaviour problems, such as aggression and rule-breaking, in both boys and girls. These early behavioural problems often overlap with oppositional defiant disorder, a condition marked by persistent anger, irritability and severe defiance toward authority figures. While this connection is often stronger in older children and teenagers, teachers can still identify these traits in children under five years old (Longman, 2015). Spotting these behaviours early allows doctors and teachers to track a child’s growth before bad habits set in.

Other child-level factors, such as high impulsivity and psychopathic traits, can make aggressive actions and delinquent behaviour worse (Del-Monte, 2016). In fact, when CU traits combine with ODD symptoms, children are at a much higher risk for chronic aggression than those showing typical defiance alone (Waller et al., 2026). However, experts stress that having CU traits as a young child does not mean a child is guaranteed to become a violent person or psychopath (Perlstein, 2023). Instead, these traits give an early warning that a child needs extra help. Finding these risky behaviours early is key to preventing bigger struggles later in life.

Albert Bandura’s social learning experiment directly demonstrates how young children aged 3-6 learn aggressive and emotional behaviours by observing adults (Bandura, 1961). In this study, researchers had over 70 preschool children individually watch an adult act aggressively toward an inflatable, weighted “Bobo doll”, punching, kicking and shouting at it, while another group observed adults playing calmly (Bandura, 1961). When left alone in a room with the same toys, the children who observed violent adults recreated the exact physical and verbal aggression, whereas children who observed calm adults showed less violent behaviour. This classic experiment showed that young children rapidly absorb and imitate social behaviour from their surroundings. Both positive and aggressive traits are shaped by the adult in the child’s early environment (Bandura, 1961).

In conclusion, research on early childhood development shows how traits such as emotional coldness and learnt behaviours shape how a child behaves as they grow. High impulsivity and a lack of empathy can lead to serious behavioural problems. These early warning signs are central to understanding ODD, as unaddressed coldness and defiance often worsen persistent angry, argumentative and disruptive behaviour. Because young children quickly pick up habits and feelings from the adults around them, early identification paired with supportive, warmth-centred parenting offers a powerful framework for intervention. By replacing ineffective punishment with positive reinforcement and emotional guidance, families and professionals can successfully guide children away from ODD and chronic behaviour issues.

2.3 Genetic and Biological Contributing Factors

Psychopathy can be detected in the brain and is characterised by structural and functional brain abnormalities in cortical (such as the prefrontal and insular cortices) and subcortical (such as the amygdala and striatum) regions, leading to neurocognitive disruptions in emotional responsiveness and reinforcement-based decision-making (De Brito et al., 2021). After MRI scans of the brains of 39 German men with a score over 20 on the Psychopathy Checklist Revised (PCR), differences were found in their brains compared to the brains of non-psychopaths. The study shows that people with high scores on the second dimension of psychopathy (the anti-social part) had smaller brain regions associated with behavioural control, such as the subthalamic nucleus, substantia nigra, thalamic nuclei and regions of the orbitofrontal cortex (Pieperhoff et al., 2025). Another study to find the differences between psychopath and non-psychopath brains found that people who had a high score on the PCR had a 10% larger stratum, which partially coordinates decision-making, motivation, reinforcement and reward perception, leading to an increased need for stimulation and proneness to boredom (Choy, Raine & Schug, 2022). The combination of these two factors leads to a person who needs more stimulation than average, will get bored with things faster and is more prone to making irrational decisions. 

Like many aspects of one’s personality, psychopathic traits can be passed down from older generations. Genes involved in the function of common neurotransmitters, such as serotonin and dopamine, can be influenced by one’s genetic background (Volk, 2024). The parental influence on these genes can lead to psychopathic traits mainly because these neurotransmitters are responsible for regulating one’s mood and reward system. For example, it is shown that individuals with psychopathic traits may have a hypersensitive dopaminergic reward system, meaning that they release much more dopamine when anticipating rewards (Buckholtz et al., 2010). This sensitivity can lead them to have a more intense drive for a certain goal. Oftentimes, this strong desire to accomplish their goal will override the risks and consequences that may occur (Salisbury, 2010). Their hypersensitive dopaminergic reward system helps to explain psychopaths’ impulsivity, intense actions and ability to overlook consequences, which in some cases can be traced back to one’s parents. 

The gene most linked to anti-social and violent behaviour is low-activity monoamine oxidase A (MAOA). MAOA releases enzymes that degrade neurotransmitters like serotonin (Kolla & Bortolato, 2020). Therefore, having low MAOA leads to less degradation of these neurotransmitters, leading to more build-up in the brain (McDermott et al., 2009). As a baby, this build-up causes some sensors to deactivate in an attempt to compensate (Krakowski et al., 2003). Having fewer receptors functioning affects a person’s ability to naturally inhibit aggressive urges. Therefore, the impulsivity linked to psychopaths may be found in very low quantities of MAOA. 

However, the inheritance of this gene goes to show further details about psychopathy. Since the MAOA gene is located on the X chromosome, the inheritance patterns differ between males and females (Baravkar et al., 2025). Men can only inherit one X chromosome therefore, if they inherit a low or high strand of MAOA, there is no other X chromosome to offset it. Contrarily, women have two X chromosomes; therefore, if they inherit a low or high strand of MAOA, it is more likely that it is offset (Chen et al., 2018). This genetic difference between males and females may lead to an understanding of why there are statistically more males exhibiting psychopathic traits than females. 

Frick and White (2008) found that CU traits are particularly important in understanding a psychopath and psychopathy in general, as they represent many emotions and interpersonal features, especially low empathy, lack of guilt and minimal emotional responses. CU traits do not automatically mean that someone is a psychopath. Consistent display of CU traits and anti-social behaviour may be an early indicator of psychopathy. Neuroscientists explain that the amygdala is the emotional centre that processes fear, distress and empathy. A psychopath’s amygdala may seem smaller than that of a normal person, and psychopaths do not respond to fear, distress or empathy. The prefrontal cortex is responsible for the mind’s critical thinking and reward system. Psychopaths do not learn from rewards and punishments. CU traits are able to remain in a stable state from childhood to adolescence; the more prominent the CU traits are, the greater the likelihood of persistent anti-social behaviour. As CU traits are not permanent, factors, parenting quality and improvements in parent-child connection can reduce their presence.

2.4 Evidence from Twin Studies

In 2010, a twin neuroimaging study was conducted that looked at the heritable variations in grey matter concentration as a potential endophenotype for psychopathic traits (Rijsdijk et al., 2010). The goal for this study was to determine whether brain abnormalities associated with psychopathic traits could be genetically influenced. The sample consisted of 123 male twins aged 10-13 years old containing 56 monozygotic (identical) and 67 dizygotic (fraternal) individuals. They were recruited through the Twins Early Development Study in England and Wales. They used structural MRI and VBM analysis to measure grey matter concentration in the subjects’ brains. Then they applied a biometrical genetic twin model which allowed them to mathematically study the variation in particular brain structures and how much could be attributed to genetic influences. The grey matter concentration in two areas associated with psychopathic traits were found to be the most heritable: the left posterior cingulate cortex (46% heritable) and the right dorsal anterior cingulate cortex (37% heritable). These regions are involved in processes such as empathy, moral processing and introspection. The researchers found that common genetic influences helped explain psychopathic traits and structural variation in different regions of the brain. 

Another twin study by Tuvblad et al. (2014) looked at the heritability of psychopathic personality traits, focusing on 14-15 year old twins. The aim of their study was to investigate the relative contribution of genetic and environmental factors to psychopathic personality traits in adolescents. They wanted to solve the problem that the earlier twin studies had, which was that estimates of heritability could depend on who assesses psychopathy and which instruments are used. To solve this, they used multiple measuring methods and multiple informants including the adolescents themselves, their parents and trained assessors. They found 604 pairs of twins, both fraternal and identical, and used methods including behavioural interviews, neurocognitive testing and psycho-physiological assessments and found that genetic influences explained 69%  of the psychopathic personality traits and non-shared environmental influences explained 31%. This study continues to demonstrate how the hereditary component associated with psychopathic traits is certainly present, but not the only contributing factor.

2.5 Parenting Styles and Practices

Another one of the many factors that can lead to a child developing psychopathic traits early in life is how they were raised. Parents have a huge impact on their children. The children’s personality development is affected by their parents’ personality and how they treat their child. The way that parents choose to treat their child, like their rules and punishments, heavily affects their lives. Some parenting styles that can lead to a child developing psychopathic traits include: permissive, authoritarian, uninvolved/neglectful, harsh/hostile and inconsistent parenting (Rousseau, 2025).

Rousseau (2025) explains that a permissive parent typically provides little to no boundaries, has low frustration control and low empathy. This type of parenting causes the child to have extremely high self-esteem and entitlement, be less responsible and be very impulsive. They have irregular emotions and trouble voicing their feelings. These children have trouble keeping friends and have low interest in academics. An inconsistent parent consistently changes their rules and has unpredictable reactions. This can lead their child to have difficulty learning clear boundaries, self-control and trust. This makes it difficult for them to keep friendships as they will consistently push others’ boundaries. 

An authoritarian parent, as Rousseau (2025) suggests, has high demands, expects blind obedience without an explanation and lacks warmth. They offer no emotional validation, which can lead their child to resent them and lack moral internalisation. These children have very low self-esteem and do not trust their own feelings. They do not get along with people easily and have poor social skills. In school, they struggle to concentrate and tend not to have any important achievements. A harsh/hostile parent frequently yells, physically punishes and intimidates their child. This shuts down any emotional connection between parent and child. This can lead to the child modelling their parent’s aggressive behaviour and lashing out at friends or during school.

An uninvolved/neglectful parent, according to Rousseau (2025), lacks warmth, attention and/or basic care for their child. This teaches their child that themselves and other people do not matter and are not deserving of affection. These children have low self-esteem, little confidence and hate themselves and/or others. They tend to hide their feelings and avoid them, leading them to be withdrawn, disrespectful and distrustful. They also perform poorly in academics. Living in neglectful environments can cause these children to develop psychopathic traits as a defence mechanism. They suppress emotional responses to cope with bad situations and abuse, and can appear cold and narcissistic to hide their fear and anxiety. This leads to a lack of empathetic traits later in life. Neglectful parenting can also result in proactive aggression (goal-oriented, intentional), which is often observed in children with psychopathic traits.

A study by Krupić et al. (2020) examined the role of parental personality traits and parenting styles in explaining psychopathic tendencies in children. 173 parents were tested, and it revealed that parental Psychopathy Resemblance Index (PRI) has both direct and indirect effects on children’s psychopathy; parental agreeableness has both direct and indirect negative effects; neuroticism through the authoritarian and permissive parenting styles has a positive indirect effect; openness has a direct negative effect; and extroversion has a direct positive effect on children’s psychopathic tendencies. Positive effects means that there is a relationship or correlation – the parental trait negatively affects children. A negative effect means there is no relationship or negative effect to the child. Thus, as Krupic et al. (2020) suggest, permissive and authoritarian parenting styles, along with other punitive behaviours, can directly contribute to the development of psychopathic traits in children. 

Overall, all of these styles of parenting are harmful to children and can lead to them exhibiting psychopathic traits early in life at a critical time of their identity development. Most personality features appear to be set by the age of eight. These children could later become psychopaths if these symptoms are not treated as soon as possible, which is less likely, if the parent’s behaviours also do not change (De Ruiter et al., 2022).

2.6 School Experiences

While psychopathic traits have been linked to biological, genetic and parenting factors, experiences during childhood may also play a significant part in their development, reinforcing these traits. Outside of family, school is known to be the most influential environment in a child’s development, shaping how they interact with others and helping them understand social relationships. From an early age, children are expected to excel academically, adapt to their social settings and create meaningful relationships. But what happens when this environment becomes a source of fear, rejection and humiliation? More importantly, could these experiences influence the development of anti-social tendencies?  

Van Geel et al. (2017) suggest that psychopathic personality traits may be an important factor in understanding bullying behaviour among young people. When a child is bullied in school, their perception of learning is negatively distorted and can lead to problems in future experiences. It can lead to distrust and social withdrawal, which results in hypervigilance and emotional numbing in later life, resembling the emotional detachment seen in psychopathy. Youths who display high levels of callous-unemotional traits may be less responsive to the fear and suffering of others and may therefore be more prone to perceiving aggression as a positive outcome (Pardini et al., 2003). This reduced sensitivity to others’ distress, combined with a tendency to use aggression instrumentally to gain dominance and popularity, may contribute to a greater likelihood of engaging in bullying, according to Salmivalli (2010). The authors also found that the relationships between bullying and both impulsivity and narcissism became stronger with age, indicating that these traits may become increasingly relevant to bullying behaviour as children grow older. Moreover, Van Geel et al. (2017) envisioned psychopathic personality as involving high levels of all three dimensions – CU traits, narcissism and impulsivity – rather than any single trait in isolation (Hare, 2003; Cooke & Michie, 2001; Fanti & Kimonis, 2012). Overall, these findings suggest that bullying may be particularly associated with a combination of emotional detachment, self-focused interpersonal characteristics and impulsive behaviour.

Building on this association, Sourander et al. (2007b) provide evidence that childhood bullying may also be linked to longer-term anti-social outcomes. Although anti-social personality disorder is not directly correlated to psychopathy, the two constructs share similar core characteristics, referring to the idea that studying ASPD is relevant to understanding the emergence of the broader psychopathy traits. In the Finnish study, titled, “From a Boy to a Man”, approximately 2,500 boys were assessed at age eight and categorised as: uninvolved, victims, bullies or bully/victims based on their experiences of bullying. Their mental health and behavioural adjustment were also assessed, and participants were followed into late adolescence. At age 18, those who had been identified as bullies in childhood had approximately three times the odds of being diagnosed with anti-social personality disorder, while those who had experienced both bullying and victimisation had around seven times the odds. Therefore, the longitudinal nature of the study suggests that involvement in bullying during childhood may be an important marker of developmental risk for later anti-social personality pathology.

Further evidence that childhood bullying may influence psychological development comes from a newer study by Tsomokos and Slavich (2024), who examined whether bullying could contribute to later mental-health difficulties through changes in interpersonal trust. Using longitudinal data from approximately 10,000 young people in the UK Millennium Cohort Study, the researchers found that being bullied at age 11 was associated with greater interpersonal distrust at age 14, which subsequently predicted higher levels of internalising and externalising difficulties at age 17. In particular, adolescents who developed greater distrust following experiences of bullying were approximately 3.5 times more likely to experience clinically significant mental-health problems than those who developed lower levels of distrust. The authors suggest that bullying may lead to future issues regarding social life, referring to the idea that young people could interpret good intentions as threatening or untrustworthy instead. This could therefore influence how they behave and interact with others, making it difficult to develop meaningful relationships. Although the study does not directly measure psychopathy, the findings may be relevant to understanding how early bullying could influence the development of psychopathic traits, as social threats may shape a young person’s mindset and contribute to distrust.

2.7 Community Violence

Growing up around chronic violence in one’s neighborhood has been consistently linked to the development of callous-unemotional traits, a key feature of psychopathy in youth. One study of serious youth offenders found that “exposure to community violence, a common and chronic experience for justice-involved adolescents, is one such traumatic event associated with callous-unemotional traits” (Loyola University Chicago, 2021). The researchers explain this through the concept of “secondary psychopathy”. While some youth may be born with an innate difficulty feeling empathy, others develop CU-like traits as a coping response, essentially “emotionally desensitis[ing]” after repeated exposure to traumatic events like community violence (Loyola University Chicago, 2021).

A related study of detained African American and Caucasian juvenile offenders found that “exposure to community violence was correlated with both psychopathic traits and emotional response to distress stimuli” (University of New Orleans, n.d), and that psychopathic traits were linked to reduced emotional responsiveness to distressing stimuli, specifically among youth with high violence exposure.

2.8 Childhood Psychopathology: Oppositional Defiant Disorder

Oppositional defiant disorder is a childhood mental health condition, often characterised by consistent patterns of an angry mood, vengeful attitudes and head-strong behaviour. As stated in the ICD-11, callous-unemotional traits can be used to identify a more severe presentation of ODD. The presence of these traits may indicate that a child’s oppositional and defiant behaviours are not simply due to poor emotional regulation or anger, but rather reflect more complex difficulties regarding emotional responsiveness and interpersonal relationships. 

A study by Hawes et al. (2017), which looked into late childhood interpersonal callousness (although not specifically ODD), shed light on how childhood behaviours could potentially contribute to later “psychopathic” traits. They used data collected from a longitudinal study on boys, with an overwhelming sample of the youth exhibiting elevated conduct issues. More specifically, the growth curve analysis used in this study indicated that initial elevated levels of interpersonal callousness (IC) and conduct problems (CP) in childhood could effectively predict the development of interpersonal and affective features of adult psychopathic behaviours. Additionally, boys at a higher initial level were at a higher risk of developing anti-social traits. The findings from this study support a developmental pathway to later issues in life (Hawes et al., 2017).

Children diagnosed with ODD are at increased risk of later developing conduct disorder, but this is not an inevitable developmental progression. Longitudinal research consistently shows that only a proportion of children with ODD progress to CD, and the strength of this association varies according to factors including sex, existing conduct symptoms and the nature and severity of the child’s behavioural difficulties. 

In the Great Smoky Mountains Study, ODD predicted later CD in boys but not girls once existing conduct symptoms were taken into account, and transitions from ODD to CD were less common than might be expected, particularly during adolescence (Rowe et al., 2010).

The risk also appears to depend on the type of oppositional behaviour the children displayed. Rowe et al. (2010) identified two distinct groups of behaviours: irritable and headstrong. Headstrong behaviours, such as persistent defiance, arguing, deliberately annoying others and blaming others, were more predictive of later CD. Irritability was more strongly associated with later emotional difficulties. On this basis, the authors suggest that children displaying headstrong ODD symptoms may be more likely to display later conduct problems and callous attitudes, while irritable symptoms were associated with depression and anxiety.

More recent longitudinal research has strengthened this developmental link. Ezpeleta et al. (2022) followed 622 children from the general population every year from age 3-12, and asked teachers to repeatedly rate three characteristics: headstrong/defiant behaviour, irritability and callous-unemotional traits. They found a reciprocal relationship between headstrong/defiant behaviour and CU traits throughout childhood: an increase in either one predicted a later rise in the other. In simple terms, when a child’s headstrong behaviour increased relative to their own usual level, their CU traits tended subsequently to increase, and vice versa. Interestingly, a different pattern was found with regards to irritability. While increased headstrong/defiant behaviour predicted increased irritability the following year, irritability did not predict later increases in headstrong behaviour or CU traits, presumably due to maturity and emotional management.

In brief, the evidence shown does suggest that conditions like ODD may form part of a developmental pathway towards more persistent anti-social behaviour, especially among children who might display CU traits. Although Hawes et al. (2017) did not examine ODD directly, their findings indicate that childhood interpersonal callousness and behavioural problems can interact to increase the risk of developing psychopathic features in adulthood. This supports the view that ODD, when accompanied by CU traits and persistent conduct problems, may represent an increased risk for later anti-social and psychopathic tendencies and behaviours.

2.9 Adolescent Psychopathology: Conduct Disorder

Conduct disorder is often seen as purely “outbursts” or “bad behaviour”, usually confused with teenage rebellion. But through thorough investigation, psychological research suggests that there are more complex factors involved. Conduct disorder is a mental disorder characterised as a repeating pattern of aggressive and rule breaking behaviour. Although negative environmental experiences can influence the disorder, researchers have increasingly investigated whether differences in brain development may also contribute to these behaviours.

A significant study by the ENIGMA Antisocial Behaviour Working Group (2026) examined MRI brain scans from 2,438 young people between the ages of 7-21. Researchers found differences in several brain regions among young people with conduct disorder compared with those without the disorder. These included the cerebral cortex, amygdala, hippocampus and thalamus. These areas are important because they are involved in emotional processing, memory, decision-making and controlling behaviour. The study also found that young people with more severe symptoms, particularly lower levels of empathy, guilt and remorse, tended to show more noticeable differences in brain structure in these regions.

These findings are important because they challenge the idea that people with conduct disorder simply choose to behave badly. Instead, their behaviour may be influenced by a combination of biological and psychological factors. For example, differences in brain areas involved in emotional processing could potentially affect how someone understands other people’s emotions or responds to certain situations. However, the research does not prove that brain differences directly cause conduct disorder. Scientists cannot yet determine whether these differences contribute to the development of the disorder or whether they may partly result from environmental experiences. More long-term research is needed to understand this relationship.

Overall, the research supports the biopsychosocial approach, which suggests that conduct disorder develops through an interaction between biological factors, psychological characteristics and environmental experiences. Understanding these different influences could help researchers develop more effective ways to identify and support young people with conduct disorder.

3. Serial Killer Profiles

When childhood psychopathic behaviours are not curtailed, aggressive behaviours can increase and, for some, lead to murder. If not caught, psychopaths’ sense of grandiosity, disdain for laws and increasing boldness to live out their fantasies and impulses result in serial killings and are labelled as such after their third victim. Psychopaths target specific victims based on particular motivations, opportunities and personal grudges.

For instance, Christine Falling preyed on young children, using her position as a babysitter to gain access to vulnerable victims aged two months to four years old. Her actions were opportunistic and driven by an inability to resist violent impulses (Campbell, 2025). In contrast, Judy Buenoaono targeted her husbands and boyfriends, as well as her own son, motivated by financial gain through life insurance payouts (Campbell, 2025). Albert Fish, however, fixated on young children and subjected them to extreme torture and cannibalism, reflecting his sadistic urges (Bosky, 2024). Jack the Ripper focused on prostitutes who were often isolated and struggled with substance abuse, suggesting a pattern of targeting those he considered powerless or disposable (Keppel et al., 2005). Ted Bundy exploited the trust of empathetic young white women aged 12-25, using his charm to fabricate helplessness to lure them in (Tabor, 2026). These patterns reveal that psychopaths often select victims based on accessibility, vulnerability or personal desires such as financial, revenge or sadistic motives.

3.1 Type of Motives

Motives play an extremely vital role in the execution of crime, especially serial murder. Drawing from the typologies devised by Dietz, Holmes, Rappaport, Sewall, Krupp and Lalumiere (Miller, 2014), four subtypes have emerged based on the similarities between the characteristics within their respective typologies. These categories differentiate the distinct motives that serial killers might possess. Importantly, these motives have derived from the behavioural typologies of serial killers, meaning that the proposed motives closely relate to the behaviour exhibited by these killers. Therefore, these categories should be understood as insights to the motives of serial killers, rather than a definitive outline for serial killing behaviour.

Sexual sadism: The harming of others, especially through torture and unconsented suffering, gives the killer complete control. This not only asserts their dominance, but also fulfills their need for self-worth, making them feel superior. As a result, the underlying motive is not only psychological gratification, but also the need for dominance (Miller, 2014).

Delusional motives: Some killers may kill in response to illusions or even hallucinations that involve the accomplishment of a “mission”. Therefore, the offender may feel as though their actions fulfilled a duty that they were obliged to do, or perhaps feel justified due to their political or religious stance (Miller, 2014).

Custodial motives: Custodial killers normally have a position of authority or responsibility within an institution, like healthcare, for example. These killers exploit those who are dependent on help, which gives them a unique position of power, with the ability to decide between life and death for their victims. The vulnerability of these victims is used against them, which satisfies the killer’s desire for power (Miller, 2014).

Utilitarian motives: Those driven by utilitarian motives use murder as a tool for their true objective, which normally involves tangible gains such as financial advantages. Murder is not used for satisfaction, like the other motives, but instead for an alternative goal. Consequently, these killers are more goal-oriented, as the kill works towards a final objective (Miller, 2014).

3.2 Signature Style

Expanding from the factors that influence one to kill, many prominent offenders adopt distinctive patterns, habits and traditions enacted during the process of taking someone’s life. These repeated actions reveal crucial information about a killer, ranging from their hidden psychological needs to how they want to be perceived by the public. These patterns can be explored in greater detail, being referred to as killer’s modus operandi, ritual or fantasy-based behaviour, and signature style. 

Modus operandi (MO), a Latin phrase, is directly translated by Merriam-Webster to a “method of procedure”. It refers to a person or group’s habitual method of doing something, such as a distinct pattern of behaviour, a style of work or a routine way of achieving a goal. It includes how an offender approaches a victim, how they gain control, what restraints are used, how detection is avoided and how the offender leaves the crime scene. As killers learn from their mistakes and change tactics, their MO is not set in stone and does not have to be identical to have been committed by the same offender.

Ritual or fantasy-based behaviour is more closely related to an offender’s psychological desires. This behaviour is enacted to provide some type of psychological satisfaction to the offender, as it is not necessary to complete the crime. This is a crucial way to learn more about the killer and find their underlying motives.

A serial killer’s signature style is a combination of these two variables, being described by psychiatrists Hazelwood and Warren as “the unique combination of behaviours suggesting that multiple crimes were committed by the same offender” (Hazelwood & Warren, 2003). In short, the modus operandi is what the killer has to do in order to commit the crime, while the signature represents what the killer psychologically wants to satisfy, by going beyond what is necessary to kill. Examining the signature behaviours of serial killers such as Dennis Rader and Jeffrey Dahmer displays how offenders can formulate patterns that reflect their fantasies and psychological wants.

Dennis Rader’s signature style involved binding, torturing and killing his victims, earning him the nickname “BTK” by the FBI. He also would photograph the crime scene while he posed with the victim. Rader would most often tie his victims up and control their access to oxygen via strangulation, leading to psychiatrist Park Dietz stating “the desire for control was central to Rader’s psychopathology” (Dietz, 2021). His repeated contact with the media and police reveal his underlying psychological need to seek the public’s attention and need for recognition. 

We also see this reveal of signature style in the infamous serial killer Jeffrey Dahmer, who kept and preserved the remains of his victims exceeding their death. Forensic psychiatrist, Dr Park Dietz, who testified for the prosecution in Dahmer’s case, stated that “what corpses, mannequins and unconscious people all have in common is they don’t make demands, they don’t complain and they don’t leave. For Dahmer, that’s the big one” (Tron, 2024). This revealed that Dahmer’s underlying motives for committing these horrific acts were related to his psychological desires for control, possession and companionship. His victims were typically, but not exclusively, boys or men. His kill was quick and he then harmed the corpse, indicating he did not want his victims to suffer, unlike sadists.

3.3 The Role of Fantasies

It is theorised that the more one’s fantasies were cognitively and carefully rehearsed, the more power the killer obtained in their own perception. MacCulloch exemplified this notion as he found a pattern of sadistic fantasies that played out repeatedly in sexual murders, which resulted in escalation in the nature of their actions (Prentky, 1989). There is also abundant support for the “high concordance between presence of deviant fantasies and occurrence of deviant behaviour”, as devised by Abel and Blanchard (cited by Prentky, 1989). The pair’s conclusion allowed the likely connection of offender categories and level of fantasy present. Although contested, the two common categories, mostly used by the FBI and criminal profilers, are organised and disorganised killers.

Organised killers are meticulous and precise with their planning, laying out their methods before the attack, as well as perhaps taking a “trophy” and leaving behind a “signature” mark at the crime scene, or on the victim themselves. Contrastingly, a disorganised killer would leave behind a rather “messy” scene, reflecting a lack of preparation and impulsivity (Ressler & Burgess, 1985). This may be evident through the use of items or weapons of opportunity rather than a crime-specific weapon and a pre-existing strategy. These killers may also kill in the “spur of the moment”, fueled by impulsivity and anger. It is hypothesised that organised murderers have a higher IQ (Prentky, 1989). But while intelligence plays a minimal part in the content or quality of the deviant fantasy, it can impact the way fantasy is mapped out into behaviour. Therefore, the organised killer may be characterised as one possessing a greater integration of fantasies into their planning and execution of murder.

In a study conducted, 86% of a serial homicide group, compared to 23% of a single homicide group, had violent fantasies, which was noted in their report (Prentky, 1989). Since trial runs and initial murders can never precisely mirror the level of satisfaction derived from the fantasy, the killer needs to restate the fantasy with a new victim. This provides a potential explanation for the escalation and continuation of murder, yet does not establish fantasy as the sole cause of violent crimes. Therefore, higher level of fantasies in serial killers means that the murder is less likely to meet their expectations, leading to a potential increase in kills. It is important to note that “normal” people can also have sexually deviant fantasies, but it does not mean that they will commit a violent crime such as murder.

4. Discussion

This research investigation aimed to understand the question: “why do some psychopaths become serial killers?”. There are many types of psychopaths, but they do not all kill. There are also many types of biopsychosocial factors that differentiate psychopaths who kill versus psychopaths that take advantage of people for their own self-interest. This literature review examined twin studies, biological studies, case studies, longitudinal studies, meta-analyses and others to answer the research question.

Biological and genetic studies strongly confirmed that psychopathy is inheritable. Psychopaths can have hypersensitive dopaminergic systems, a hereditary trait, that can explain why psychopaths will go farther to achieve their goals. This leads to impulsivity and overlooking consequences. They also have low MAOA, which indicates high risk-taking behaviours and a lower ability to naturally control their aggressive urges. This hereditary trait is more common in men than women. Twin studies verified that the two areas of the brain responsible for empathy, moral processing and introspection were structurally and functionally different in psychopaths and serial killers. This is presumed to be a result of abnormal development in early childhood, more likely due to neglect and abuse, reflecting 69% genetic and 31% environmental causes.

Brain development that cannot experience empathy and moral decision-making may express a key indicator of psychopathy: callous-unemotional traits. While some can display these without being a psychopath, what differentiates normal mood swings from a psychopath through CU traits is repetition and patterns. If someone consistently displays these traits, it can lead to the assumption of psychopathy. These traits include, but are not limited to: lack of guilt, shallow empathy, lack of remorse, minimal concern for consequences, minimal distress sensitivity, very minimal interpersonal skills and manipulation of others to get what one desires.

Emotional control is another behavioural marker of psychopaths and serial killers. Some psychopaths have enough self-control not to lash out in severe anti-social ways, such as killing people. Those scoring above 30 (out of 40) on the PCR are predicted to have less self-control and consideration of consequences, leading to an increased probability of killing. Psychopaths with a high score in the second dimension of psychopathy are shown to have smaller brain areas connected to behaviour control and a decreased ability to think about the consequences of their actions. 

Environmental factors that appear to have a strong influence on activating psychopathic genes involve parenting styles, trauma/abuse and mental health disorders. Harmful parenting styles that can result in reactive and hostile behaviours growing up include: permissive, authoritarian, uninvolved/neglectful, harsh/hostile and inconsistent parenting. When parental behaviours become abusive and result in trauma, due to physical, emotional and sexual abuse, harsh or unnecessary punishments, or exposure to violence (domestic or community), they can change the structure of the child’s brain, central nervous system and bring out CU traits. The impact of these parenting styles  on a child are a lack of empathy, lashing out, difficulty keeping friendships, being withdrawn, avoiding their feelings, not caring about themselves or others, irregular emotions, trouble voicing their feelings, risk-taking, aggression, disruption, and defiant behaviours with lower empathy, guilt and remorse. Sustained behaviours through childhood can lead to the development of oppositional defiant disorder and, in adolescence, conduct disorder that can predict anti-social personality disorder in adulthood in which psychopathy can turn to serial killing.  

In adulthood, psychopaths that become serial killers often act on hidden psychological desires and motives that drive their violent behaviours (Fox & DeLisi, 2018). These desires may include the need for power, control and even a twisted sense of companionship which they seek to fulfill with their crimes (Fox & DeLisi, 2018). Many serial killers crave public recognition and attention, going as far as to photograph their victims or send messages to the media to ensure notoriety or memorialise their crimes (Olivier, 2007). Others are driven by a desire to assert dominance not just in the act of killing but in the aftermath by keeping the remains of their victims, allowing them to maintain a form of control and possession even after their victims’ deaths (Warren et al., 2013). This behaviour reflects the inability to form genuine relationships as the killer clings to these remains to satisfy a need for connection and power.

Overlapping theories have constructed distinct typologies that help us better understand the motives of serial killers. They include: sexual sadists with the desire to harm others, assert their dominance and achieve a sense of dominance and superiority: delusional killers who are motivated by illusions or hallucinations, political or religious in nature; custodial killers who harm others through their position of authority; and utilitarian killers who use murder as the first step to a greater goal, such as financial gain. Therefore, why psychopaths kill is strictly personal and derived from unmet needs.

The motivation to kill often starts from fantasies, envisioning how it will be done and the gratification that will be achieved, driving the motivation and cognitive sense of power higher until a person acts out their fantasies. There are organised and disorganised serial killers and a prediction of a higher level of intelligence in organised types, who are more difficult to track and find. Their signature styles reflect identities they often use to taunt police. Fantasists construct their planned and organised crime to a high degree. Disorganised killers are led by impulsive, often spontaneous and erratic behaviours that can explain the mistakes they make and evidence they leave behind after their crime. Over two-thirds of serial murderers’ first sexual homicides were organised, compared to only one-quarter of sexual homicides committed by single murderers being organised.

5. Conclusion

In conclusion, research suggests that some psychopaths become serial killers because of a complex mix of biological, psychological, developmental and environmental factors. Psychopathy alone does not mean that a person will commit heinous crimes, violence or murder. However, characteristics such as callous-unemotional traits, reduced empathy, lack of remorse, impulsivity and difficulty considering consequences can increase vulnerability to anti-social and violent behaviour. Research into genetics and neuroscience also suggests that differences in brain development, reward systems and inherited traits genetics are only part of the explanation, with environmental influences also playing an important role. 

Childhood experiences can further influence how these traits are developed. Harmful parenting, neglect, abuse, bullying, exposure to community violence and persistent behavioural problems may contribute to emotional detachment and anti-social behaviour. However these experiences do not guarantee that a child will become a psychopath or serial killer. As these individuals slowly develop, psychological factors such as fantasies, motives or the desire for control, recognition or personal gratification may influence whether violent behaviour becomes repeated. The different motives and signature behaviours found among serial killers demonstrate that there is no single pathway to serial murder. 

Therefore, the answer to the research question, “why do some psychopaths become serial killers?”, has no single cause. Instead, serial killing appears to result from the interaction of individual vulnerabilities with developmental experiences and psychological motivation. Understanding these factors is important to challenge the stereotype that every psychopath is inherently violent, as well as highlighting the importance of early identification and intervention. By recognising concerning patterns of behaviour and understanding the different influences that contribute to them, researchers and psychologists may be better able to develop interventions and family treatments to prevent harmful behaviour from escalating in the future.

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