Operation Devil Horns was a four-year-long criminal investigation run by Homeland Security Investigations (HSI), culminating in the arrests and convictions of more than three dozen members of the MS-13 gang in San Francisco. It is one of the largest such cases of its kind in U.S. history.
San Francisco was governed at the time (2004 – 2008) by a sanctuary city policy first adopted in 1989 by the city's board of supervisors, which strictly prohibited local police officers from cooperating with federal immigration law enforcement. This situation was significant because many of the gang members targeted by Operation Devil Horns were not citizens of the United States and thus were subject to possible deportation to their home countries in Central America.
Numerous of the criminal defendants in the case argued during their trials that they were victims of illegal entrapment by the federal investigators in Operation Devil Horns, stemming from the actions of criminal informants who were controlled by HSI agents. However, this legal defense strategy ultimately proved unsuccessful in all but one minor case.