This article studies the international determinants of extrajudicial police killings in Latin America. Human rights violations by security forces are a problem that has plagued Latin American countries, despite broad democratization efforts in the region. Addressing the problem requires a better understanding of the processes that underlie it. Although existing literature has explored the determinants of police repression in Latin America through country-specific studies, there has been a lack of cross-national analyses. In this article we use original data on human rights violations by security forces in Latin America between 1998 and 2018 to argue that, beyond domestic factors, foreign aid provided by the United States in the War on Drugs era has influenced police repression both by encouraging heavy-handed policies and by driving a substitution dynamic between violations by different security forces.