Abstract: In criminal cases, decision-makers aim to selectively incarcerate defendants with a high risk of future violent crime. If decision-makers have more accurate beliefs about this risk, can they reduce violent crime without simply incarcerating more defendants? We survey 162 prosecutors about how violent re-arrest rates vary across defendants of different ages and with different criminal records. We link prosecutors’ beliefs to their 104,039 cases, which offices assign quasi-randomly. Prosecutors’ beliefs vary widely and predict their sentencing patterns for defendants of different ages and criminal records. Prosecutors with more accurate beliefs (by one standard deviation) reduce violent crime (by 6%) without incarcerating more defendants.