Abstract The aim of this paper is to identify the factors associated with the performance of police internal affairs divisions. Little is known about the performance determinants of organizations crafted to prevent deviant behavior of civil servants. To reach our goal, we analyzed 797 administrative proceedings against 1.195 military police of a given Brazilian state between 2005 and 2012. Our quantitative analysis demonstrated that cases involving more experienced police officers and crimes with increased complexity are less likely to be concluded. Our results also suggest that social norms and internal codes inherent to police forces affects the extent of punishment to implicated officers: some crimes seem to be tolerated while others are abhorred by the police force. Surprisingly, an increased centralization in the investigative activity is not associated with increased efficiency of the investigation process. Actually, investigation commissions formed by police officers specialized in investigating their own peers are less likely to have their cases concluded or to condemn police officers. Our results contribute to theoretical debates on the design of watchdog organizations and the literature on organizational performance of accountability bodies.