["Criminology &Public Policy, Volume 25, Issue 1, Page 89-112, February 2026. ", "\nAbstract\n\nBackground\nMexico rolled out state‐led criminal justice reforms between 2000 and 2017 to modernize procedures and improve rule of law. Whether these changes reduced violent crime—especially in cartel‐affected areas—remains uncertain.\n\nAims\nEstimate the impact of reform implementation on homicides and arrests, and assess mechanisms related to enforcement capacity and public cooperation with law enforcement.\n\n\nMaterials & Methods\nWe build a municipality–year panel (2000–2017) from death certificates (homicides) and administrative records (arrests). Because states adopted reforms at different times, we use difference‐in‐differences estimators designed for staggered adoption and heterogeneous treatment effects, with rich fixed effects and controls. To probe mechanisms, we analyze nationally representative survey measures of crime reporting, institutional trust, and perceived police/prosecutorial integrity.\n\n\nResults\nReform implementation is associated with a ~25% increase in homicide rates. Over the same horizon, arrest rates fall by >50%. As homicides are less prone to underreporting than other crimes, the homicide increase is unlikely to be a reporting artifact. Survey evidence shows reduced crime reporting, declining trust in institutions, and more negative views of police and prosecutors; effects are strongest in cartel‐affected regions.\n\n\nDiscussion\nThe pattern is consistent with an erosion of effective enforcement capacity at rollout: fewer arrests and lower public cooperation raise expected returns to violent crime. In high‐violence settings, reforms that change procedures without parallel boosts to investigative and prosecutorial capacity—and without safeguards for witnesses—can weaken deterrence.\n\n\nConclusion\nMexico’s staggered judicial reforms coincided with higher homicides and sharply lower arrests. Successful reform in violent contexts likely requires coordinated institutional strengthening (policing, prosecution, witness protection), phased implementation with measurable benchmarks, and strategies to sustain public trust and reporting.\n\n"]