Angelo Zappalà

Behavioural crime linking in serial homicide

Abstract The present study aimed to identify dimensions of variation in serial homicide and to use these dimensions to behaviourally link offences committed by the same offender with each other. The sample consisted of 116 Italian homicides committed by 23 individual offenders. Each offender had committed at least two homicides. As some offenders had worked together and some murders involved more than one victim, there were 155 unique pairings of offenders and victims. Dichotomous variables reflecting crime features and victim characteristics were coded for each case. Using Mokken scaling, a nonparametric alternative to factor analysis, seven dimensions of variation were identified. Five of the dimensions described variations in the motivation for the killings. Three of these were concerned with aspects of instrumental motivation whereas two of the motivational scales described variations in sexual motivation. The two remaining dimensions dealt with the level of planning evident in the crime scene behaviour of the offender. Two dimensions were identified: one consisting of behaviours suggesting a higher level of control and another describing impulsiveness. Using discriminant function analysis with the dimensions as independent variables and the series an offence belonged to as dependent variable, 62.9% of the cases could be correctly assigned to the right series (chance expectation was 6.2%). The implications of the results for serial homicide investigations are discussed.

Assessment of sexual interest using a choice reaction time task and priming: A feasibility study

Purpose. We investigated the feasibility of assessing sexual interest in hetero- and homosexual men using two information-processing methods, namely a choice reaction time task and priming. The participants were expected to have longer reaction times for sexually explicit when compared with non-explicit pictures due to sexual content-induced delay. In addition, the reaction times of the heterosexual (N=15) and homosexual (N=11) men for pictures corresponding with their sexual interest were compared to pictures not corresponding with their sexual interest. Heterosexual men were expected to have longer reaction times during the presentation of sexually explicit female as opposed to male pictures, whereas homosexual men were expected to have the opposite pattern. Method. The participants were presented either sexually explicit or non-explicit male and female target pictures (and primes that preceded the targets in random combinations) while simultaneously performing a choice reaction time task in three phases each containing a total of 160 prime–target pairs. Results. Both expectations were confirmed in phase 1 of the study. In phase 2, the means differed in the expected way, but the effects were not significant. In phase 3, the expected effect was moderated by a complex priming effect. Conclusions. The results suggest that the choice reaction time task is a promising way of measuring sexual interest but that questions of habituation should be given more attention in future studies.

Distance travelled and offence characteristics in homicide, rape, and robbery against business

Purpose. We aimed (1) to describe distances from home to offence locations (journey-to-crime) of offenders in difficult-to-solve homicides and rapes as well as robberies against businesses; (2) to see whether the distances in these offences differ from each other; and (3) to test whether selected features related to the offence would be associated with the distances. Methods. Lists of difficult-to-solve (DTS) homicides (N = 99) and rapes (N = 56) as well as robberies against businesses (N = 275) from the city of Milan (Italy) were acquired. The collected data consisted of home and offence location coordinates with information on the behaviour of the offenders (for rapes and homicides). The journey-to-crime functions were calibrated using the journey-to-crime module of CrimeStatIII©. Results. Most distances were short. In homicides, distances were below 1 km, in rapes below 2 km whereas in robberies against businesses almost 6 km. Some crime features were correlated with the distances in rape and homicide cases. Combining the behavioural information to a spatial behaviour measure allowed for better prediction of travelled distances compared to using single variables. Conclusions. The results have practical implications for crime investigations as the crime features explored were, as a rule, such that they would be known by the police prior to the offender being identified. A general theoretical framework for binding together journey-to-crime distances and offender crime scene behaviour and other important crime features is needed.

The virtual people set: developing computer-generated stimuli for the assessment of pedophilic sexual interest.

The implicit assessment of pedophilic sexual interest through viewing-time methods necessitates visual stimuli. There are grave ethical and legal concerns against using pictures of real children, however. The present report is a summary of findings on a new set of 108 computer-generated stimuli. The images vary in terms of gender (female/male), explicitness (naked/clothed), and physical maturity (prepubescent, pubescent, and adult) of the persons depicted. A series of three studies tested the internal and external validity of the picture set. Studies 1 and 2 yielded good-to-high estimates of observer agreement with regard to stimulus maturity levels by two methods (categorization and paired comparison). Study 3 extended these findings with regard to judgments made by convicted child sexual offenders.

Identifying Pedophilic Interest in Sex Offenders Against Children With the Indirect Choice Reaction Time Task

Pedophilia – a disorder of sexual preference with primary sexual interest in prepubescent children – is forensically relevant yet difficult to detect using self-report methods. The present study evaluated the criterion validity of the Choice Reaction Time (CRT) task to differentiate between a sample of child sex offenders with a presumably high rate of pedophilic individuals and three control groups (other sex offenders, non-sex offenders, and community controls, all male; N = 233). The CRT task required locating a dot superimposed on images depicting men, women, girls, or boys and scrambled pictures as quickly as possible. We used two picture sets, the Not Real People (NRP) set and the Virtual People Set (VPS). We predicted sexually relevant pictures to elicit longer reaction times in interaction with the participant group. Both CRTs showed main effects of stimulus explicitness and preferred stimulus gender. The CRT-NRP also yielded an interaction effect of participant group and stimulus maturity while the CRT-VPS showed a tendency in this direction. The overall effect size was moderate. Results offer support for the usefulness of the CRT task in forensic assessment of child sex offenders.

Simulations of child sexual abuse interviews using avatars paired with feedback improves interview quality

We tested whether simulated child sexual abuse (CSA) interviews with computer-generated child avatars could improve interview quality. Feedback was provided not only on question types, as in previous research, but also on whether the conclusions drawn by the interviewers were correct. Twenty-one psychology students (average age M = 24.5) interviewed four different avatars which had a simulated story of either abuse or non-abuse. The participants were randomly divided into two groups: one received feedback on question types and conclusions after each simulated interview and the other one did not receive any feedback. Avatars revealed pre-defined ‘memories’ as a function of algorithms formulated based on previous empirical research on childrens suggestibility. The feedback group used more open-ended and fewer closed questions. They also made more correct conclusions and found more correct details in the last two interviews compared to the no-feedback group. Feedback on both the question types and conclusions in simulated CSA interviews with avatars can improve the quality of investigative interviews in only one hour. The implications for training practice were discussed.

Differentiating sexual preference in men: using dual task rapid serial visual presentation task

Cognition research suggests that allocating attention resources to evolutionarily relevant stimuli is facilitated suggesting that sexual stimuli interfere with human information processing. In a group of gay (n = 13) and straight men (n = 13) recruited in Finland, Germany and Italy, we investigated if and how sexually relevant visual stimuli affect information processing of both a target one (T1) and a subsequent target two (T2) in a dual target rapid serial visual presentation procedure. We hypothesized that: (1) due to the attentional blink (AB) phenomenon, the accuracy of reporting of T2 would decrease when following accurately identified sexually preferred T1 compared to accurately identified non-sexually preferred T1; 2) due to the pop out effect, the accuracy of reporting of T1 and T2 would be relatively increased when T1 and T2 were sexually preferred by the participants compared to when they were not. Our findings did not support hypothesis 1 but supported hypothesis 2. We further found that the pop out effect had a good capacity to differentiate sexual preference between the groups of gay and straight men. We conclude that dual target rapid serial visual presentation can be used as an attention-based measurement to differentiate sexual preference in men. Limitations and the applicability in the field of measuring sexual preference were discussed.

Using a Dual-Target Rapid Serial Visual Presentation Task (RSVP) as an Attention-Based Measurement Procedure of Sexual Preference: Is it Possible to Fake?

As faking threatens the validity of sexual preference measurements in forensic contexts, we investigated in an analogue study the fakeability of the dual-target Rapid Serial Visual Presentation (RSVP), an attention-based measurement procedure. In the dual-target RSVP, when observers attempt to detect two targets (T1 and T2) in a stream of stimuli presented in rapid succession, identification of T2 is impaired when it follows T1 within approximately 500 ms, a phenomenon called Attentional Blink (AB). Emotional stimuli result in an “emotion-induced blindness” or “attentional rubbernecking” effect: AB increases (detection of T2 decreases) when T1 is salient and decreases (detection of T2 íncreases) if T2 is salient or when participants are concurrently engaged in distracting mental activity. The participants were 9 gay men, 8 straight men, and 12 straight men with the last group instructed to fake their T2 responses assuming the expected response style of gay men when the T1 and T2 stimuli were pictures of nude and clothed men and women. We found differences in the reporting of both T1 and T2 between the gay men and the faking straight men as a function of the type of T1 resulting in good differentiation between the two groups (AUC = 0.78–0.92). The results suggest that the different patterns of reporting are in most explainable by a combination of the increase in cognitive load in the faking group and of the subtlety of the attentional effects of whether the stimuli were intrinsically of sexual interest to the participants. We conclude that the RSVP as an attention-based measurement procedure of sexual preference has a moderate resilience to faking. The generalizability of these findings to forensic contexts should be further explored.

Can hard-to-solve one-off homicides be distinguished from serial homicides? Differences in offence behaviours and victim characteristics

Purpose – The purpose of this paper is to explore the differences (if any) between serial and hard-to-solve one-off homicides, and to determine if it is possible to distinguish the two types of homicides based on offence behaviours and victim characteristics. Design/methodology/approach – A sample of 116 Italian serial homicides was compared to 45 hard-to-solve one-off homicides. Hard-to-solve one-off homicides were defined as having at least 72 hours pass between when the offence came to the knowledge of the police and when the offender was caught. Logistic regression was used to predict whether a killing was part of a series or a one-off offence. Findings – The serial killers targeted more strangers and prostitutes, displayed a higher level of forensic awareness both before and after the killing, and had more often an apparent sexual element in their offence. Conversely, the one-off homicides were found to include more traits indicative of impulsive and expressive behaviour. The model demonstrated a goo...

Identifying deviant sexual interest in a sex offender sample using dual-target rapid serial visual presentation task

Abstract To investigate the dual-target rapid serial visual presentation (dtRSVP) task as a measure of deviant sexual interest (i.e. a sexual interest in children), we administered a dtRSVP with gender- and age-specific pictorial stimuli to child sex offenders (n = 69), other sex offenders (n = 43), non-sex offenders (n = 14), and community controls (n = 88). We hypothesized that (1) stimuli belonging to the preferred gender and age group presented as targets (both T1 and the subsequent T2) in the serial sequence would be more accurately detected than non-preferred stimuli and that (2) this increased detection would reduce the detection of targets later in the serial sequence (T2) due to an attentional blink. Our findings supported hypothesis 1 and partly supported hypothesis 2. Although we found group differences, individual indices based on detection rates did not allow for individual-level diagnostic categorization of participants.