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Biased decision-making in criminal investigations can impede or arrest the progress of justice. Previous research has not systematically addressed the effects of professional experience on the quality of detectives’ decision-making. Using a quasi-experimental design, this study compared the quality of investigative decisions made by experienced detectives and novice police officers in two countries with markedly different models for the development of investigative expertise (England and Norway). Participants (N = 124) were presented with two semi-fictitious cases and were asked to report all relevant investigative hypotheses and necessary investigative actions in each case. The quality of participants’ responses was gauged against a gold standard established by a panel of senior homicide experts. In the English sample, experienced detectives vastly outperformed novice police officers in the number of …