From the U.S. to Mexico: Tracing the Flow of Illicit Firearms across the Border
Capstone Thesis by Claire Castrejon and Abigail Tank, Georgetown University
May 2026
Abstract: This capstone examines the origins, pathways, and consequences of U.S.-sourced firearms recovered in Mexico, drawing on firearm trace data obtained from the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) through a Freedom of Information Act (FOIA) request.
Employing a mixed-methods approach that integrates geospatial analysis, quantitative data, and a structured review of existing literature, this study maps the geographic distribution of traced firearms at the U.S. ZIP code level and analyzes their relationship to major transportation infrastructure across the 2015-2024 study period.
The findings reveal that the majority of traced firearms originated in Texas and Arizona, with a notable shift towards Arizona beginning in 2019, a pattern this capstone links to demand-side changes in Mexican trafficking networks, particularly the rise of fentanyl corridors along the Sinaloa-Sonora-Arizona axis and shifting cartel territorial dynamics.
Time-to-crime analysis further indicates that a significant share of recovered firearms were purchased and deliberately diverted from legal markets. Situating these findings within broader scholarship on U.S. firearm policy, Mexican legislation, militarization, and cycles of violence, this capstone argues that the flow of U.S. firearms into Mexico constitutes a transnational human rights crisis that cannot be addressed through domestic or militarized solutions alone.
In response, this capstone proposes four policy recommendations: implementing universal background checks, increasing outbound border inspections, returning oversight of small arms exports to the U.S. Department of State, and repealing the Tiahrt Amendments.
This project was conducted in partnership with Global Exchange’s Stop U.S. Arms to Mexico initiative and under the supervision of Professor Jenny Guardado at Georgetown University’s Walsh School of Foreign Service.
Interactive Map of Firearms Traced from Mexico to United States, 2015-2024
