Recent evidence emphasizes the significance of procedural justice in fostering trust in the police. However, the empirical research primarily derives from aggregated national data, focusing on major cities, and predominantly in the global north. In regions affected by armed conflicts in the global south, I argue that trust between citizens and the police is driven by endogenous factors, such as effectiveness and fear of crime; exogenous factors, like rurality; and social mechanisms, like leadership. To examine this, I collected novel data from nine municipalities in Colombia, employing three methods: i) 5,929 snowball sampling surveys targeted at key informants, ii) a probabilistic survey representing 145,000 citizens, and iii) a two-year fieldwork period. The findings yield four unconventional results. Firstly, in remote areas grappling with armed conflict in the global south, effectiveness emerges as the primary influencing factor for trust in the police. Secondly, citizens residing in rural regions exhibit lower trust in the police, while leaders and critical informants in these areas express higher levels of trust, emphasizing the importance of effectiveness. Third, leaders and critical informants generally display higher levels of trust in the police and acknowledge the inherent clash of interests between the police and the local state, challenging prevailing literature that assumes their alignment. Finally, there are differences in the distribution of trust, depending on the type of illegal armed group in dominance. This thesis underscores the relevance of utilizing disaggregated local data to comprehend institutional trust.