Identifying Criminal Career Patterns of Sex Offenders

Intense social and political changes in the past decades led to changes in crime rates and the way the public perceives crime. Although there is a concern about crime in general, there seem to be some types of offences that cause more distress to the general public than others, for example, sexual offences. They seem to receive significant amounts of public condemnation and represent the focus of many punitive policies. In order to understand criminality as an individual and a social problem, researchers began to study crime through the concept of criminal career. One of the ways of getting insight into this type of offenders is by exploring their criminal career referring to a longitudinal series of offences committed by a person which has a noticeable series of offences. The study of the criminal career of sexual offenders has the potential to bring new information to experts and legislators, contribute to a greater understanding of the continuity of transgression from adolescence to adulthood and ensure better knowledge of the occurrence of sexual misconduct, how it begins, how it develops over time and how it ends.


Introduction
In a never-ending pursuit to understand individual criminality and how various social factors encourage or inhibit criminal activity, criminologists developed the concept of criminal careers [1,2]. This concept emerged from the work of Alfred Blumstein [3], who aimed to quantify offending and improve the way criminology and other behavioural and social sciences make prediction and test empirical data. Using data from previous research, Blumstein et al. developed a concept of "criminal career" in order to develop a framework through which effective crime control policies could be developed [4]. Their understanding of the concept developed from indicating individual offending frequency (λ) calculated by determining the average number of crimes committed per year by active offenders (true frequency) measuring the individual arrest frequency (the average number of arrests per year of active offenders; measured frequency -the μ). They determined that λ and μ were linked by q, a probability of arrest following a crime (μ = λ * q) (μ = λ * q) [4].
At the same time, in the 1980s, the US showed an intense social and political focus on high crime rates and crime control. Due to the rise in violent crime, the US Government started a task force on violent crime which proposed increasing the federal role in the prosecution of violent crime, and other far-reaching changes in federal law including abolishing parole, expanding prisons, and restrictions

Aetiology of sex offending
In the past, sex offender literature has largely focused on biological and psychological roots of offending making individual pathologies and early trauma the most common explanations for sexual offending. Traditional theoretical views on sexual offending describe sexual offending through trait-like features such as cognitive distortions, low victim empathy, deviant sexual preferences, poor attachment style, sexual regulation. We will here briefly present some of the most used theoretical explanations regarding sex offending.
One of the major concept used in explanations of sexual offending is paraphilias who are defined as sexual disorders characterised by intense, sexually arousing fantasies involving either nonhuman objects, suffering or humiliation of oneself or one's partner, children or other nonconsenting persons [11]. Most common paraphilias are paedophilia, voyeurism, transvestic disorder and exhibitionism [12]. However, it was found that unlike problems such as depression or anxiety, most cases of sexual offending (rape, child molestation, etc.) are not associated with any particular cluster of covarying signs and symptoms [13]. Moreover, even though some individuals who commit sexual offences against children are diagnosed with paedophilia, a mental disorder characterised by deviant sexual interests in children and some may have a paraphilia of some type, typically, this is not the case for all child sex offenders. [13]. Attachment theory, however, points out that sexual deviance is a consequence of the loss or emotional distress and intimacy deficits [14].
The psychodynamic theory explains sexual deviance as an expression of the unresolved problems experienced during the stages of development, and sexual deviancy occurs when the id is overactive [14]. The function of id is to operate unconsciously and to impel the organism to engage with need satisfying activities which are experienced as pleasure. However, this explanation fails to address the cultural context of human development [15]. Similarly, biological theories focus on abnormalities in the structure of the brain, level of hormones, genetics, and deficits in the intellectual functioning of sex offenders. Many studies have shown abnormalities in the brain of some perpetrators, but there is insufficient evidence to support more generalisation of the results [16].
Sex offending can also be studied through feminist theories focusing on the structure of the relationship between the sexes and the disparity of power between a man and a woman [16]. In general, feminist theories on child sexual abuse are divided into radical feminist perspective and post-modern perspective. Radical perspective centres on the patriarchal nature of (Western) society. Patriarchy has been defined by radical feminists as the world view that seeks to create and maintain male control over females. This perspective emphasises that sexual abuse is a representation of the patriarchy and the power that men have over women and that all men are socialised to hold attitude and exhibit behaviours that are associated with sexual offending. However, this perspective was criticised because of the lack of empirical scope [17]. The post-modern perspective rejected the radical perspective and established that men who sexually abuse are neither outside the society nor reducible to it and that they may know exactly what they are doing, but some offenders may not. This perspective was as well criticised because it is vague on what their theoretical position on sexual violence is [17].
Evolutionary theories, however, explain the diversity of human behaviours, including the aggression of sexual offenders as a way of adapting to changes in the environment. The evolutionary settings explain sexual aggression on sexual selection and reproductive strategies, whereby as one of the sexual strategies they cite the compulsion of sexual coercive is also present in the animal world as one of the reproductive strategies. The criminal offence of rape within these theories is a result of the inability of men to win a partner by more appropriate methods [16].
More influential theories in social sciences described sexual offending through cognition and behaviour. Behavioural theories suggest that deviant sexual behaviour is the result of learned behaviour. They assume that sexual excitement plays a crucial role in sexual offences. Sexual satisfaction and lack of negative consequences of sexually deviant behaviour increase the likelihood that such behaviour will continue. If the negative effects are strong enough, the behaviour will decrease [16]. However, many male sex offenders lack deviant sexual arousal patterns [18] and other traits such as the lack of empathy for the victim or remorse which in some individuals may also play a role in the development of deviant sexual behaviour patterns [16].
Cognitive theories suggest that cognitive distortions are the main cause of deviant sexual behaviour and that "concealed" opinion leads to "distorted" behaviour [16]. Cognitive distortions are often referred to as offence-supportive attitudes, or cognitive processing during an offence sequence, as well as post-hoc neutralisations or excuses for offending [19]. The cognitive-behavioural theory addresses how offenders' thoughts affect their behaviour: focus on how sexual offenders diminish their feelings of guilt and shame by rationalising them through excuses and justification [14]. Although many offender rehabilitation programmes focus on eliminating cognitive distortions, the relationship between cognitive distortions and future crime is not clear and it seems cognitive distortions may not be what causes fallacious thinking at all because, outside the criminal context, "making excuses" for one's behaviour is widely viewed as a normal thing [19].
Social learning theories explain how children who are victims of sexual abuse become perpetrators of sexual offences as adults. Also, this theory states that sexually explicit materials can contribute to committing sexual offences. Furthermore, victim's age at the beginning of abuse, the relationship between the perpetrator and the victim, the type of sexual act, the amount of coercing used, and the duration and number of victimising events all have a crucial role in the connection of acts of sexual offences and subsequent acts of sexual delinquents [16]. This theory is most often criticised because there is little evidence to suggest that children who are victimised will become abusers themselves [20]. Furthermore, direct link between the use of pornography and sexual violence was never confirmed; however, some studies suggest there might be some connection between pornography and attitudes that support sexual aggression [16].
One of the limitations of these trait-like approaches is that it comes at a cost of a broader view of sexual offending. Moreover, individual pathologies-based explanations are not well suited for a developmental and longitudinal perspective of causes for this kind of behaviour. They have also contributed to sex offender researchers emphasising the differences, rather than searching for the similarities between sexual and nonsexual offending [6]. Criminal career approach provides a more developmental point of view explaining how sexual offending starts, develops, and stops as well as whether such distinctions are theoretically, clinically, and/or policy relevant [2]. In other words, maturation and dynamic theories assume that the same mechanisms underlie the behaviour of all offenders while life-course criminology emphasises the need to use a more broader view on the causes of sex offending as well as to find similarities between the perpetrators of these crimes rather than differences. The most important theoretical question that needs to be answered when studying sex offenders through criminal careers is whether sex offenders should be regarded as similar or different from non-sexual offenders in terms of the aetiology of their offending behaviour. Consequently, there are two possible ways to consider sexual offending-that it is different from non-sexual offending and that it is an integral part of the general offending repertoire.
If studied separately, one possibility is to distinguish adolescence-limited from persistent sex offenders. This way of studying offenders gained its popularity in the 1990s with Moffit's Dual Taxonomy theory [7]. This theory states that adolescencelimited antisocial behaviour individuals have brief criminal careers, lack consistency in their antisocial behaviour across situations and may also have irregular, crime-free periods. Adolescence-limited delinquents are likely to engage in antisocial behaviour in situations where they estimate they could gain profit, but they also abandon antisocial behaviour when prosocial behaviour is more rewarding.
Adolescence-limited offenders usually start offending by the ways of three distinctive conditions: motivation, social mimicry and reinforcement. Social mimicry is a term taken from the ethology and is loosely connected to the social mirroring theory. Adolescents often mimic the behaviour of their life-coursepersistent peers in order to gain the same benefits (i.e., status in the peer groups; friends, etc.). In other words, adolescence-limited offenders commit criminal offences if they can gain from them, and if such behaviour is reinforced by their peers. With a change in their circumstances, for example, starting college or starting a job, they will usually stop offending [7].
Individuals that fall under the category of life-course-persistent antisocial behaviour exhibit antisocial behaviour at an early age. For example, biting and hitting at age 4, shoplifting and truancy at age 10, selling drugs and stealing cars at age 16, robbery and rape at age 22, and fraud and child abuse at age 30; the underlying disposition remains the same, but its expression changes form as new social opportunities arise at different points in development. The Dual taxonomy theory, however, does not suggest that all specific behaviours in childhood will be predictive of criminal behaviour in adulthood, but that it might be associated with behaviours that are conceptually consistent with the earlier behaviour [7].
Beyond young adulthood, the antisocial disposition of life-course-persistent may be expressed in a form that is not yet well-measured (e.g. neglect and abuse of family members). According to this theory, it is necessary to investigate the roots of antisocial behaviour in the early life of life-course-persistent offenders. Moreover, some of the causes for life-course-persistent offending are neuropsychological (disruption in the ontogenesis of the fetal brain, minor physical anomalies, maternal drug abuse, poor prenatal nutrition, exposure to toxic agents, brain injury because of complication during delivery), variability in infant temperament, developmental milestones and cognitive abilities, exposure to criminogenic environment or inconsistent discipline. Thus, over the years, an antisocial personality is slowly constructed. Likewise, deficits in language and reasoning are incrementally elaborated into academic failure and insufficient job skills. Over time, all the problems accumulate, and an individual has fewer options for change. This theory of lifecourse-persistent antisocial behaviour emphasises the constant process of reciprocal interaction between personality traits and environmental reactions to them [7].
However, if sex offending is studied combined, the question is to what extent sexual offending (or which type of sexual offending) is characteristic of a particular overall offending trajectory. Furthermore, it might be necessary to study sexual offenders by dividing them into different offence types as they may be stemming from different causal processes and thus it would be best to consider their different developmental pathways [6]. Current research suggests that there are some significant differences between sex offenders and non-sexual offenders. For example, the prevalence of general delinquency peaks in adolescence while sex offenders have two peaks in offending, one in adolescence and on in the mid to late 30s [6,21,22]. Also, sex offenders show continuity in general offending and antisocial behaviour, but low continuity in sexual offending [22]. This finding resonates with the finding that delinquency is usually just a part of a larger behavioural repertoire consisting of potentially harmful behaviours such as substance misuse [21]. Similarly, non-sexual offences usually precede sexual offences and specialisation in sex offending does not increase in adulthood [6,22]. Therefore, criminal career offers an interesting way of studying offending patterns by looking into the four key dimensions (participation, frequency, seriousness, and length [3,4,9,10,23] and related constructs such as escalation, specialisation, co-offending, intermittency, and others [2,9,24,25].

Participation and frequency
The dimension of participation refers to the proportion of a population who are active offenders at any given time, while frequency refers to the average annual rate at which this subgroup of active offenders commits crimes. In other words, participation refers to the prevalence of offending, while frequency refers to the incidence of crime [26]. Both dimensions are particularly difficult to research and estimate because of the underreporting of sexual offences and the so called "dark figures" of crime. Nevertheless, frequency has been of particular interest to the policymakers as it implicated that it is possible to identify high-frequency offenders and incapacitate them to maximise the incapacitation effect. However, it appears that the frequency of offending is very complex and that its value might fluctuate throughout a criminal career [27]. Another difficulty with the dimension of frequency is that it is challenging to estimate. For instance, one sex offender can offend against one victim over a, for example, 5-year period, multiple times, but official reports will note his offences as one offence.
The Cambridge study [28] found that the prevalence and frequency of sex offending in community samples is low and that that there is little evidence of recidivism or continuity. With respect to the prevalence and frequency of sex offending, conviction data indicated that whereas 41% of the males in the sample had been convicted by age 50, only 2.5% of the males had a conviction for a sex offence.
However, self-report and victimisation studies show a much higher number of individuals participating in sexual offending. For instance, The Bureau of Justice Statistics' (BJS) in the US conducts a National Crime Victimisation Survey (NCVS) [29] every year using a nationally representative sample of 240,000 interviews on criminal victimisation. Results for 2018 showed that the rate of rape or sexual assault victimisation increased 1.6 to 2.7 victimizations per 1000 individuals aged 12 or older in comparison to previous years. Even more concerning data emerged from two meta-analyses [30,31] of 282 studies around the world on child sexual abuse. The analyses used self-report data and found that the prevalence of child sexual abuse ranges from 12.7-19.7% for girls and 7.6-7.9% for boys. Both analyses showed that the highest prevalence of sexual abuse of children is in Africa and the lowest prevalence rate in Europe.
It is important to point out that sexual offences are often generalised as heterosexual offence [32] and therefore, there is very little known about male victims [33]. Recent figures indicate that around 12,000 males are victims of sexual assault or rape in the UK every year [34] and that nearly 1 in 4 men in the U.S. experienced some form of contact sexual violence in their lifetime. Among male victims of complete or attempted rape, about 71% experienced such victimisation before the age of 25 [35].
The frequency of offending varies significantly depending on the used method and between types of sex offenders. Sex offenders against women have, on average, 1.8 victims, whereas extra-familial child abusers have 3.4 victims on average [36]. Another study [37] suggests that sexual offenders with adult women victims had, on average, 2 official victims, but self-reported close to 12 victims. Similarly, sex offenders who offended against children had, on average, officially offended against 2 victims, but self-reported 7 victims.
Finally, investigations into the frequency of prolific, persistent sex offenders using several sources of information (i.e., self-reports, police investigations, victim statements) came up with three key conclusions on sex offending [38]. Firstly, about 11% of the sample committed over 300 sex crime events as opposed to about 40% who committed only one sex crime event. Secondly, some offenders take advantage of low-risk short-term opportunities with different victims, while others exploit a single offending opportunity by repeatedly offending against the same victim over a certain period of time. Thirdly, the findings revealed that the most prolific sex offenders were older, had a more conventional background characterised by a stable relationship with an adult partner, a job at the time of the offence (s), no drug issues, and no prior record for a sex crime.

Seriousness
The third dimension of the criminal career, seriousness, is in some ways, fundamental for criminal career research. Seriousness refers to the level of seriousness of the offences being committed by a given individual [3] and takes the modern approach to crime by focusing on determining a level of risk. Risk relates to the probability of criminal behaviour and is usually measured as low, moderate, or high [39,40]. Offender risk is usually determined based on the possibility of reoffending or recidivism. It is important to define two categories here: chronic and recidivists [41]. The chronic type offenders are more at risk of persistent life-span criminal careers, which are costlier to society; over time they may have more victims (and financial loss for the victims) in addition to the costs associated with their arrest and incarceration. Recidivists are less persistent, as they have a lower incidence of reoffending. However, the categories do not differentiate on the severity of offences, only on offending timespan.
Offenders that maintain lengthier periods of offending tend to be generalists in their criminal behaviour [42,43], their offences may be less severe than those that commit more severe types such as rape, sexual homicide, or child abuse. While there may be differences between types of reoffences (i.e. fraud and sex offences), society is risk-averse to more salient offences such as rape and child molestation [44,45]. However, meta-analyses reports show that public fear of sexual offenders is often misplaced, and that offender's recidivism rates for sexual offences vary between 11,5% and 13,7% while general recidivism rate varies between 33,2% and 36,2% [46,47].
Some authors argue that these four key dimensions of criminal career, and especially seriousness, made it possible for a variety of important theoretical opportunities to emerge along with research on criminal careers [48]. This segment of criminal careers has several parameters that are observed through the dimension of seriousness: the severity of the criminal offence, escalation, specialisation, and crime-type switching [49].

The severity and escalation
The severity of the offence refers to the tendency towards committing severe criminal offences during a criminal career while escalation refers to the tendency towards making initial minor offences towards the increasingly more severe offences [27]. Escalation reflects the concern that as the career develops, the offender engages in more serious offences. There are different causes for escalation, for example, experience, increasing boldness or a stressful experience [6,27].
Escalation research emerged interesting findings such as that most sex offenders who perform masturbation in front of their victim do not switch to a different sexual act (for example intercourse) when they abuse their second victim [50]. This finding points out that sex offenders tend to specialise in a particular sexual act and that they are not likely to escalate their sexual offending from non-contact to contact offending, for instance.
Another interesting finding [51] suggested that victim resistance plays a significant role in whether or not offenders will de-escalate in the amount of physical force used between victims. If the first victim resisted the offender, he was more likely to de-escalate in the level of physical force used. However, if the second victim resisted, the offender was less likely to de-escalate, indicating that he is adopting more force to secure subsequent victims if there is resistance. Furthermore, sex offenders who consume drugs in the hours before the first crime are more likely to de-escalate in the level of physical force used than be stable.
Crucial to determining behaviour consistency is the way an offender sources his victims. The "hunting" process is an essential stage of the sexual assault and offenders who find their victims through their relationships, or their occupation will often repeat their behaviour in their future crime. In contrast, offenders who find their victims more spontaneously are less likely to repeat this "hunting" method [52].

Specialisation and crime-type switching
Specialisation is an aspect of criminal careers and is defined as likely repetitions of the same type of criminal offence [23] while versatility reflects a tendency to commit a broad array of offences without concentrating on a specific behaviour. Researchers use a "crime-switch" matrix, a matrix of crime types reflecting the probability that an offender who has previously committed one crime type will next commit a different type [27]. Research showed that there is a relationship between higher frequency of offending and versatility, but also that offenders who start offending at an early age tend to be involved in a diverse array of offences [6]. Most criminal careers are diverse, but there is some evidence of specialisation [21].
Sex offenders in specific show little empirical evidence of specialisation, but they are characterised by persistent criminal activity and tend to show criminal diversity in non-sexual crime types [53]. It was also found [54][55][56] that there are substantial differences between sex offenders regarding victim type. Sexual offenders against adults have more versatile criminal records [54][55][56], are more violent and have a higher frequency in offending [56] than abusers of children. The other group tends to be more specialised, have a higher frequency of sexual crimes, but also tend to be criminally versatile [45][46][47][48][49][50][51][52][53][54][55][56]. Extrafamilial child molesters are consistently found to specialise more in sexual offences [54,55]. Overall, neither child abusers nor sex offenders against adult women have a specific type of victim and that the majority of both types typically commit more non-sexual offences than sexual [56].

Career length
The last dimension of criminal career research is the length; that is the time that an individual is actively offending. Research on the dimension of length attracted the attention of the scholarly community from the very beginning of criminal career research. It incorporates three head characteristics of criminal careers: beginning ("onset" or "initiation"), duration and end ("desistance" or "termination") [2,10].
The relationship between age and crime is of an asymmetrical bell shape (most commonly known as the "age-crime curve"), showing that the prevalence of offending tends to increase from late childhood, peaks in the teenage years (around ages [15][16][17][18][19], and then declines from the early 20s, often with a long tail [22]. Most offenders desist during late adolescence and early adulthood, irrespective of the age of onset [22], but an early age of onset appears to be connected to a relatively long criminal career [6,50]. Research on recidivism shows that sexual offending decreases with age, as well as general offending, and the recidivism of sexual offenders that offend against adult decreases from early adulthood [57,58]. However, unlike the general offender, sexual offenders usually start committing offences either in adolescence or in mid to late 30 [2,59].
Some of the possible explanations of why sex offenders appear to be older when they start offending include that there is a high rate of unreported sex offences because the victims are less likely to report sexual offences than non-sexual offences and because there is a disbalance between official statistics and self-report. A gap between the age of onset in the official statistics and self-report is seven years [2]. Moreover, nearly 20% of sexual offenders are at the end of their criminal career, or their career has already desisted when they are convicted of their first sexual offence [2].
Alternatively, some authors [60] suggest that the discrepancy that goes against the logic of the life-course explanation of desistance could be explained by increased average ages of marriage and parenthood. In specific, the peak in sexual offending seems to occur at a time when adolescents already transitioned into adulthood which could mean that sex offenders do not transition into adulthood at the same pace as non-sexual offenders, or that these transitions do not affect recidivism in the same way as they do non-sexual offenders. Besides the transition into adulthood, several other reasons could influence individuals to start with sexual offending. For example, loneliness is commonly reported among sex offenders, that the transitions that influence common crime do not affect sexual offending (or affect it to a lesser extent), a cost-benefit analysis that makes sex offenders less likely to accept the cost of being labelled as a sex offender, conflicting interpersonal relationships, and maturation factors [60].
The above-described factors could affect the length of a criminal career, but the most significant variable affecting the length of a criminal career is the age of the first conviction. The likelihood of termination of offending is noticeably different as the age of the first conviction rises, and more severe offenders cease to offend after the first conviction only in fewer cases [61].

Conclusion
The dynamic concept of criminal careers empowered researchers to develop a whole new way of looking at crime. Traditional criminological theories offered a rather static explanation of one's criminal conduct, while criminal career concept offered a view on criminal conduct that can be used to explain crime on an individual and group level. Furthermore, based on that, a new set of criminological theories emerged based on that concept, a Developmental and Life-Course Criminology, which emphasise a more dynamic approach to the aetiology and phenomenology of criminal conduct.
The main advantage of the criminal career concept regarding criminal conduct is that it offers a different perspective on criminality which can be used as a "bridge" between theoretical criminology and policy-relevant research. As we have shown on the example of perpetrators of sexual offences, there are differences in the development and peculiarities of the criminal career of these perpetrators. What the theories based on the concept of criminal career can offer are different explanations of the aetiology and phenomenology of these perpetrators about the particularities of their individual criminal careers. In this way, perpetrators can be viewed in terms of similarities and differences in the dimensions of a criminal career which can have multiple benefits. Specifically, although it is the same group of criminal offences, it is possible to have different theoretical explanations for the emergence and development of particular subgroups of perpetrators of certain criminal offences. In this way, specific prevention policies can be created that can be more effective because they identify not only the factors that influence the occurrence and development of certain types of crimes, but also the dynamics of the relationship between risk and protective factors that contribute to it. In this way, interventions at any level in terms of prevention and rehabilitation of offenders can be more successful.
Another great advantage of the concept of criminal career is that it allows the creation of new explanations of the origin and development of certain crimes, which contributes to the development and emergence of new criminological theories and concepts that, taking into account traditional explanations of crime and achievements of criminological research, could contribute to a new theory by erasing the understanding of committing crimes within the concepts of "traditional" and "newer" theories, but finding new ones that can merge all previous concepts into one that best suits the specifics of a particular crime or perpetrator.
It appears that only fractions of the concept and DLC theories are seldomly studied, causing the lack of comprehensive theory and resulting in some aspects of criminal careers not being researched enough while other areas are receiving more focus. This is true if we look at the types of crimes that are the focus of research under the concept of criminal career. The commission of sexual offences is now relatively unexplored and research to date has covered a small number of countries, mostly in the developed countries of the west. Therefore, the findings mentioned in the chapter need to be considered from the context of these countries. We hope that there is going to be more international collaboration and more scholarly focus on this topic in the years to come.