In the weeks following the 2019 murder of an Amsterdam lawyer, a case widely linked by the media to the so-called «Mocro Mafia» and Moroccan-Dutch crime networks, Dutch judges imposed significantly harsher prison sentences, averaging 71% longer, on suspects of Moroccan descent, while sentences for others remained unchanged. These were the findings of a recent joint study by the University of Gothenburg, Vrije Universiteit Amsterdam, and Erasmus University Rotterdam. Researchers attributed this pattern to the «salience effect», a psychological bias where judges unconsciously give greater weight to certain characteristics, in this case, ethnic background, when these are highly publicized. The murder in question was that of Derk Wiersum, a Dutch lawyer fatally shot outside his Amsterdam home while representing Moroccan-Dutch state witness Nabil B. in the high-profile Marengo trial against the so-called «Mocro Mafia» led by Ridouan Taghi. According to the study, the effect applied to 384 Moroccan-origin defendants, whose sentences increased by roughly three months. Once media attention faded, sentencing levels returned to normal. The phenomenon was most evident among judges with less experience handling cases involving Moroccan suspects. The researchers emphasized that judges acted within the bounds of the law but suggested implementing peer reviews or automated comparison systems to ensure fair sentencing in the wake of major societal shocks. Wiersum's killers, neither of Moroccan descent, were sentenced to 30 years in prison, a verdict upheld on appeal in 2023.
