["Criminology &Public Policy, Volume 21, Issue 3, Page 489-534, August 2022. ", "\nAbstract\n\nResearch Summary\nDe‐prosecution is a policy not to prosecute certain criminal offenses, regardless of whether the crimes were committed. The research question here is whether the application of a de‐prosecution policy has an effect on the number of homicides for large cities in the United States. Philadelphia presents a natural experiment to examine this question. During 2010–2014, the Philadelphia District Attorney's Office maintained a consistent and robust number of prosecutions and sentencings. During 2015–2019, the office engaged in a systematic policy of de‐prosecution for both felony and misdemeanor cases. The city recorded the fewest number of criminal prosecutions in modern history, with a 70% reduction in the number of criminal sentencings. Philadelphia experienced a concurrent and historically large increase in homicides. This article employs a difference‐in‐differences analysis using a synthetic control method to estimate the effects of de‐prosecution on the number of homicides in Philadelphia. The potential donor pool is composed of the prosecutors’ offices for the 100 largest cities in the United States over a 10‐year period, with a quantitative categorization of the prosecutors’ offices used both as a variable and to exclude cities that may have been subject to a similar de‐prosecution treatment. The synthetic control model estimates that de‐prosecution has been associated with a statistically significant increase of 74.79 homicides per year in Philadelphia during 2015–2019.\n\n\nPolicy Implications\nAs various prosecution policies such as de‐prosecution are being implemented across the United States, such policies should be tested for downstream results. The broadscale de‐prosecution policy of Philadelphia—particularly for firearm and drug trafficking offenses—appears to have a causal association with a large increase in homicides. The public in Philadelphia will have to make a normative choice between a reduction in the number of prosecutions and an increase in homicides. The government of Philadelphia may consider whether significantly decreased prosecutions by the district attorney's office should result in a decrease in the budget for those services. The overall relationship between de‐prosecution and homicides should be reviewed by prosecutors across the nation for consideration in exercising their prosecutorial discretion, given unique local considerations in each jurisdiction.\n\n"]