Guiding prosecutorial decisions with an interpretable statistical model

After a felony arrest, many American jurisdictions hold individuals for several days while police officers investigate the incident and prosecutors decide whether to press criminal charges. This pre-arraignment detention can both preserve public safety and reduce the need for officers to seek out and re-arrest individuals who are ultimately charged with a crime. Such detention, however, also comes at a high social and financial cost to those who are never charged but still incarcerated. In one of the first large-scale empirical analyses of pre-arraignment detention, we examine police reports and charging decisions for approximately 30,000 felony arrests in a major American city between 2012 and 2017. We find that 45% of arrested individuals are never charged for any crime but still typically spend one or more nights in jail before being released. In an effort to reduce such incarceration, we develop a statistical model to help prosecutors identify cases soon after arrest that are likely to be ultimately dismissed. By carrying out an early review of five such candidate cases per day, we estimate that prosecutors could potentially reduce pre-arraignment incarceration for ultimately dismissed cases by 35%. To facilitate implementation and transparency, our model to prioritize cases for early review is designed as a simple, weighted checklist. We show that this heuristic strategy achieves comparable performance to traditional, black-box machine learning models.