Testing the Assumption of Behavioural Consistency in a New Zealand Sample of Serial Rapists

<p>One of the assumptions that underlies the profiling process is that criminals are behaviourally consistent from one offence to another. To date, however, this is an assumption that has not been scientifically validated. The present study therefore tested the assumption of behavioural consistency in serial rape offences. The author collected dichotomous data on 30 behavioural variables for a total of 439 offences committed by 121 serial rapists in New Zealand. There were two main research aims of the study. The first aim was to test the behavioural consistency of a range of individual behaviours. It was hypothesised that higher consistency would be found for behaviours that reflected a degree of planning or that prioritised control of the victim and the offence environment, because these behaviours might be less affected by environmental factors. In contrast, many sexual behaviours arise directly out of offender-victim interactions and therefore are most affected by environmental factors such as victim resistance. It was therefore also hypothesised that sexual behaviours would display lower consistency. A consistency measure was used that compared behaviour in consecutive offences. Consistency for each behaviour was defined as present-present or absent-absent matches of that behaviour in consecutive offences. The degree of consistency for any behaviour will be reflected in the consistency score received by that variable based on the number of matches for that behaviour across the offence series. The consistency analysis found moderate to high levels of consistency for the majority of individual behaviours. As predicted, higher consistency was exhibited for behaviours that prioritised control of the victim and the offence environment, and lower consistency was exhibited for the sexual behaviours. The second research aim was that if behavioural consistency was found in the results of the consistency analysis, to explore whether there were any underlying patterns to the consistency of offending behaviour. A factor analysis of the consistency scores established that there are clear patterns to the behavioural consistency of offenders consistent with previous analysis of offence characteristics. The factor analysis resulted in three themes or domains to behaviour: hostility, involvement and control. These findings have theoretical implications for the assumption of behavioural consistency in serial rapists, for the concepts of modus operandi and signature in offence behaviour, and for the theoretical understanding of the profiling process. The findings also have practical implications for the practice of profiling and case linkage in New Zealand, and raise possibilities for future directions in research.</p>

Testing the Assumption of Behavioural Consistency in a New Zealand Sample of Serial Rapists

<p>One of the assumptions that underlies the profiling process is that criminals are behaviourally consistent from one offence to another. To date, however, this is an assumption that has not been scientifically validated. The present study therefore tested the assumption of behavioural consistency in serial rape offences. The author collected dichotomous data on 30 behavioural variables for a total of 439 offences committed by 121 serial rapists in New Zealand. There were two main research aims of the study. The first aim was to test the behavioural consistency of a range of individual behaviours. It was hypothesised that higher consistency would be found for behaviours that reflected a degree of planning or that prioritised control of the victim and the offence environment, because these behaviours might be less affected by environmental factors. In contrast, many sexual behaviours arise directly out of offender-victim interactions and therefore are most affected by environmental factors such as victim resistance. It was therefore also hypothesised that sexual behaviours would display lower consistency. A consistency measure was used that compared behaviour in consecutive offences. Consistency for each behaviour was defined as present-present or absent-absent matches of that behaviour in consecutive offences. The degree of consistency for any behaviour will be reflected in the consistency score received by that variable based on the number of matches for that behaviour across the offence series. The consistency analysis found moderate to high levels of consistency for the majority of individual behaviours. As predicted, higher consistency was exhibited for behaviours that prioritised control of the victim and the offence environment, and lower consistency was exhibited for the sexual behaviours. The second research aim was that if behavioural consistency was found in the results of the consistency analysis, to explore whether there were any underlying patterns to the consistency of offending behaviour. A factor analysis of the consistency scores established that there are clear patterns to the behavioural consistency of offenders consistent with previous analysis of offence characteristics. The factor analysis resulted in three themes or domains to behaviour: hostility, involvement and control. These findings have theoretical implications for the assumption of behavioural consistency in serial rapists, for the concepts of modus operandi and signature in offence behaviour, and for the theoretical understanding of the profiling process. The findings also have practical implications for the practice of profiling and case linkage in New Zealand, and raise possibilities for future directions in research.</p>

Behavioural Consistency and Offender Characteristics: Investigating Modus Operandi Patterns in Serial Stranger Sex Offences

Case linkage is a statistical technique which connects multiple sexual assault cases to a single perpetrator and holds promise for informing criminal investigations. Further, examining the behaviours executed most consistently across serial offences committed by a given offender is crucial to linking offences. The current study investigated behavioural consistency in a sample of 49 male serial stranger sexual offenders responsible for 147 offences. For each offence, four crime aspects were identified: 1) pre-crime facilitators, 2) victim selection and characteristics, 3) approach and attack methods, and 4) crime scene characteristics. Consistency between and within each crime series and across offender types based on background characteristics was examined. Results indicated a high degree of behavioural consistency across all crime aspects. Behaviours occurring prior to the offence were particularly useful in establishing consistent offending patterns. The implications of these findings in the context of police investigations and their utility for clinical practice are discussed.

Behavioural Consistency and Offender Characteristics: Investigating Modus Operandi Patterns in Serial Stranger Sex Offences

Case linkage is a statistical technique which connects multiple sexual assault cases to a single perpetrator and holds promise for informing criminal investigations. Further, examining the behaviours executed most consistently across serial offences committed by a given offender is crucial to linking offences. The current study investigated behavioural consistency in a sample of 49 male serial stranger sexual offenders responsible for 147 offences. For each offence, four crime aspects were identified: 1) pre-crime facilitators, 2) victim selection and characteristics, 3) approach and attack methods, and 4) crime scene characteristics. Consistency between and within each crime series and across offender types based on background characteristics was examined. Results indicated a high degree of behavioural consistency across all crime aspects. Behaviours occurring prior to the offence were particularly useful in establishing consistent offending patterns. The implications of these findings in the context of police investigations and their utility for clinical practice are discussed.

Behavioural flexibility and reputation formation

Limited flexibility in behaviour gives rise to behavioural consistency, so that past behaviour is partially predictive of current behaviour. The consequences of limits to flexibility are investigated in a population in which pairs of individuals play a game of trust. The game can either be observed by others or not. Reputation is based on trustworthiness when observed and acts as a signal of behaviour in future interactions with others. Individuals use the reputation of partner in deciding whether to trust them, both when observed by others and when not observed. We explore the effects of costs of exhibiting a difference in behaviour between when observed and when not observed (i.e. a cost of flexibility). When costs are low, individuals do not attempt to signal that they will later be trustworthy: their signal should not be believed since it will always pay them to be untrustworthy if trusted. When costs are high, their local optimal behaviour automatically acts as an honest signal. At intermediate costs, individuals are very trustworthy when observed in order to convince others of their trustworthiness when unobserved. It is hypothesized that this type of strong signalling might occur in other settings.

Case linkage in Australian serial stranger rape

Purpose Case linkage theory and practice have received growing empirical support; however, they have yet to be examined fully within Australia. For sexual assault case linkage to be successful, it is assumed that a serial rapist will behave relatively consistently across offences yet distinctively compared to other offenders. The purpose of this paper is to test the underlying principles of case linkage, behavioural consistency and distinctiveness, as well as distinguishing accuracy. Design/methodology/approach In total, 250 solved stranger rapes by 171 offenders (46 serial rapists, 125 one-off rapists) were taken from Queensland Police Service (QPS) crime records. All possible crime pairings were created and cross-crime similarity was assessed using Jaccard’s coefficient. Receiver operating characteristics (ROC) analysis was used to examine the ability to distinguish between linked and unlinked offence pairs. Findings Serial linked pairs had the highest Jaccard’s coefficient (0.456), followed by non-serial unlinked (0.253) and finally, serial unlinked pairs (0.247). Within the ROC analysis, an area under the curve value was found of 0.913, indicating excellent distinguishing accuracy. Both the underlying principles of behavioural consistency and distinctiveness were supported through theoretical and practical methods. This paper provides the first analysis of serial rape case linkage in Australia, adding validity to this practice. Research limitations/implications The authors wish to acknowledge the support and assistance from the QPS in undertaking this research. The views expressed in this publication are not necessarily those of the QPS and any errors of omission or commission are the responsibility of the authors. Practical implications This paper provides validity to the practice of case linkage using a database within Australia. The results of this paper can be used to inform investigators of serial offender behaviours. The theories of offender consistency and distinctiveness are supported, highlighting the importance of behavioural evidence for practitioners. This paper provided a practical increase of the quantity and quality of offences uploaded on the Australian violent and sexual crimes database, which will assist further linkage efforts. Originality/value This paper is the first in Australia to examine consistency, distinctiveness and case linkage of serial stranger rape. Thus is contributes significantly not only to an increased understanding of serial rape and case linkage in Australia but also brings Australia closer to modern research practices in this field.

Geographical, temporal and individual factors influencing foraging behaviour and consistency in Australasian gannets

Foraging is a behaviour that can be influenced by multiple factors and is highly plastic. Recent studies have shown consistency in individual foraging behaviour has serious ecological and evolutionary implications within species and populations. Such information is crucial to understand how species select habitats, and how such selection might allow them to adapt to the environmental changes they face. Five foraging metrics (maximum distance from the colony, bearing from the colony to the most distal point, tortuosity index, total number of dives and mean vectorial dynamic body acceleration were obtained using GPS tracking and accelerometry data in adult Australasian gannets ( Morus serrator ) from two colonies in southeastern Australia. Individuals were instrumented over two breeding seasons to obtain data to assess factors influencing foraging behaviour and behavioural consistency over multiple timescales (consecutive trips, breeding stages and years) and habitats (pelagic, mixed pelagic and inshore, and inshore). Colony, breeding stage and year were the factors which had the greatest influence on foraging behaviour, followed by sex. Behavioural consistency, measured as the contribution of the individual to the observed variance, was low to moderate for all foraging metrics (0.0–27.05%), with the higher values occurring over shorter timescales. In addition, behavioural consistency was driven by spatio-temporal factors rather than intrinsic characteristics. Behavioural consistency was higher in individuals foraging in inshore than pelagic habitats or mixed pelagic/inshore strategy, supporting suggestions that consistency is favoured in stable environments.