Ghost guns and crime: a tale of two California cities.

Background: Privately made firearms (PMFs) or "ghost guns" are homemade, unserialized, untraceable firearms that have been increasingly used in violent crime in the United States. Very little is known about the types of PMFs recovered by law enforcement agencies and the crimes associated with these recoveries. This lack of information limits effective violence prevention policies and practices. Comparative analysis of PMF recoveries in specific cities helps clarify whether local PMF patterns and characteristics vary or reflect more general trends. This research advances epidemiological understanding of emergent violent gun injury prevention challenges by identifying variations in recovered PMF types and use in violent, drug, and weapon-related offenses in Los Angeles and San Diego, California.

Methods: Conjunctive analysis of case configurations (CACC) identifies patterns among observations (i.e., case configurations) and calculates their probability associated with a given outcome. CACC was used to identify the most common types of PMFs recovered by the Los Angeles (LAPD) and San Diego (SDPD) police departments. For each department and offense type, case configurations with above-average probabilities of offense involvement were determined. Comparisons across departments were made to identify similarities and differences in PMF characteristics and usage.

Results: PMFs were more likely to be involved in violent and weapon-related offenses in Los Angles but more likely to be involved in drug-related offenses in San Diego. In both cities, the 9 mm Polymer 80 handgun was the dominant PMF. However, 9 mm handguns were most likely to be involved in weapon-related offenses in Los Angeles compared to 0.40 handguns in San Diego. Furthermore, large-caliber handguns tended to display above-average probabilities of involvement in violent and drug offenses in Los Angeles. Long guns were represented in case configurations with above-average probabilities of involvement in substantive crimes, including violence.

Conclusions: Comparative analyses of PMF recovery patterns in Los Angeles and San Diego reveal meaningful contextual variations in PMF characteristics and suggest intentional firearm type selections by offenders. The results support increased regulation of PMFs and highlight the importance of efforts to identify and disrupt the illicit supply of large-caliber PMF handguns and PMF long guns.