Approximately one third of the global prison population is in pretrial detention, waiting for trial. Overreliance on pretrial detention exposes defendants to harsh conditions, exacerbates jail overcrowding, increases recidivism, and favors criminal governance. What policies can resource-strapped countries implement to effectively address excessive pretrial detention? Based on a theoretical model focused on institutional-level efforts, we evaluate an experimental intervention implemented in El Salvador intended to increase pretrial release requests and reduce pre-trial detention. The intervention randomly assigned public defenders to receive specialized legal training, an improved interview protocol, material resources, and increased communication channels. We find that this inexpensive, scalable program increased pretrial release requests from public defenders by nearly 10% (0.228 standard deviations) and increased the success in securing pretrial release by 4.4% (0.114 standard deviations). Heterogeneous treatment effect analyses suggest that the program increased strategic litigation among the most experienced public defenders and has distinct effects for those accused of minor and severe crimes. We find no evidence that the mechanism explaining our results involves changes in public defenders’ attitudes or perceptions about their work environments. Criminal justice programs focusing on pretrial detention may help reduce prison overcrowding in high crime countries.