To investigate the effects of selection and group socialisation on support of human rights, moral reasoning and prejudice in police officers in Taiwan. We used a longitudinal quasi-experimental design to track three cohorts of police officers (n = 585) and a comparison group of criminology undergraduates (n = 43). There were no statistically significant differences in measures of human rights, moral reasoning and prejudice between new police recruits and the control group. However, time in police education was associated with a statistically significant reduction in police officer support of human rights, moral reasoning and an increase in prejudice. In the control group, the reverse was true. Exposure to police education in Taiwan resulted in police officers being significantly more prejudiced and significantly less adherent to the principles of human rights and moral reasoning. These results appear to be attributable to police socialisation rather than selection effects.