We investigate the relationship between inter-jurisdictional cooperation and law enforcement in Mexico. Exploiting a Regression Discontinuity Design in close municipal elections, we study how improved opportunities for cooperation in crime prevention among neighboring municipalities - proxied by their degree of political alignment - may result in lower rates of violent crime. We find that municipalities in which the party in power in the majority of neighboring jurisdictions barely won experience significantly lower homicide rates during the mayor’s mandate than those in which it barely lost. This effect is sizeable and independent of which party is in power in the neighboring municipalities.