Why do users continue to contribute to darknet Child Sexual Abuse Material forums? Examining social exchange, social capital, and social learning explanations using digital forensic artifacts.

BACKGROUND: The darknet hosts an increasing number of hidden services dedicated to the distribution of child sexual abuse material (CSAM). Given that by contributing CSAM to the forum members subject themselves to criminal prosecution, questions regarding the motivation for members contributing to darknet CSAM forums arise. OBJECTIVE: Building on insights gained from research into clearnet communities, here we examine the extent to which social incentives generated by the online CSAM community may explain members' posting behavior on darknet CSAM forums. PARTICIPANTS AND SETTING: We analyze digital forensic artifacts on the online behavior of members of a darknet CSAM forum that was shut down by law enforcement agencies in July 2015. METHODS: We apply group-based trajectory modelling (GBTM), social network analysis, and mixed-effect survival models. RESULTS: Applying GBTM three posting trajectories can be distinguished. Social network analyses finds the reply network to be more centralized than predicted by chance. Mixed-effect survival models show positive associations between the length of members' first post and the time since members' first registration on the forum and subsequent posting. Contrarily, the number of replies received appears to mitigate subsequent posting. CONCLUSIONS: Findings show posting activity on the forum to be concentrated in a minority of forum members who show posting trajectories that are both frequent and persistent. Results further suggest persistence in posting is motivated by social identity and, to a lesser extent, differential association processes.

Language Dependency of /s/ Production: Native Dutch Versus Non-Native English.

With forensic recordings being collected in multiple languages increasingly often, this study investigates the language dependency of the voiceless alveolar fricative /s/ in speakers of native (L1) Dutch and non-native (L2) English. Due to phonetic similarity between the languages, Dutch learners of English may exhibit language-independent /s/ acoustics, making it an interesting feature for multilingual forensic speaker comparisons (FSCs). However, the findings show that out of the four spectral moments, center of gravity, standard deviation (SD), skewness, and kurtosis, only SD remained stable across the languages; the other measurements were language-dependent. The results were largely independent of the /s/ tokens' contexts, although an interaction between language and context was found for skewness and kurtosis: With a labial right phonetic neighbor, language dependency was largely reduced. The findings have implications for FSCs: as /s/ is language-dependent in speakers of L1 Dutch and L2 English, it shows limited potential for cross-linguistic speaker comparisons in forensic casework.

The language dependency of /m/ in native Dutch and non-native English.

In forensic speaker comparisons, the current practice is to try to avoid comparisons between speech fragments in different languages. However, globalization requires an exploration of individual speech features that may show phonetic consistency across a speaker's languages. We predicted that the bilabial nasal /m/ may be minimally affected by the language spoken due to the involvement of the rigid nasal cavity in combination with a lack of fixed oral articulatory targets. The results show that indeed, L1 Dutch speakers (N = 53) had similar nasal formants and formant bandwidths when speaking in their L2 English as in their native language, suggesting language-independency of /m/ within speakers. In fact, acoustics seemed to rely more on the phonetic context than on the language spoken. Nevertheless, caution should still be exercised when sampling across languages when the languages' phoneme inventories and phonotactics show substantial differences.

Long-term within-speaker consistency of filled pauses in native and non-native speech.

Filled pauses are widely considered as a relatively consistent feature of an individual's speech. However, acoustic consistency has only been observed within single-session recordings. By comparing filled pauses in two recordings made >2.5 years apart, this study investigates within-speaker consistency of the vowels in the filled pauses uh and um, in both first language (L1) Dutch and second language (L2) English, produced by student speakers who are known to converge in other speech features. Results show that despite minor within-speaker differences between languages, the spectral characteristics of filled pauses in L1 and L2 remained stable over time.

Foreign DNA in cosmetic gel nails.

In this case study it was investigated whether foreign DNA may get encapsulated in a cosmetic gel nail. It was inspired by a murder case in which the main suspect claims that he was wrongly convicted. Most of the evidence in the case was circumstantial. The most direct piece of evidence was DNA of the suspect found beneath the victim's fingernails. According to the prosecution and the judges, the DNA meant that the suspect had murdered the victim. However, according to the suspect, the fact that his DNA was found could be explained by a physical altercation between him and the victim 17 days prior to the murder. In that alternative scenario, the suspect's DNA became encapsulated in the victim's gel nails and remained there up until her death 17 days later. In this article, we describe an experiment designed to assess the plausibility of the alternative scenario. In the experiment we tested whether foreign DNA could be recovered in gel nails of four female individuals two weeks after transfer. In six out of eight hands the profile of the donor could be detected. Hence, in situations resembling the circumstances of this case study, the encapsulation of DNA in a gel nail prior to the attack of interest must be considered.

Cross-linguistic filled pause realization: The acoustics of uh and um in native Dutch and non-native English.

It has been claimed that filled pauses are transferred from the first (L1) into the second language (L2), suggesting that they are not directly learned by L2 speakers. This would make them usable for cross-linguistic forensic speaker comparisons. However, under the alternative hypothesis that vowels in the L2 are learnable, L2 speakers adapt their pronunciation. This study investigated whether individuals remain consistent in their filled pause realization across languages, by comparing filled pauses (uh, um) in L1 Dutch and L2 English by 58 females. Next to the effect of language, effects of the filled pauses' position in the utterance were considered, as these are expected to affect acoustics and also relate to fluency. Mixed-effects models showed that, whereas duration and fundamental frequency remained similar across languages, vowel realization was language-dependent. Speakers used um relatively more often in English than Dutch, whereas previous research described speakers to be consistent in their um:uh ratio across languages. Results furthermore showed that filled-pause acoustics in the L1 and L2 depend on the position in the utterance. Because filled pause realization is partially adapted to the L2, their use as a feature for cross-linguistic forensic speaker comparisons may be restricted.