The gang takedown was conducted by the city's police department, Los Angeles County sheriff's deputies, the FBI and the Bureau of Alcohol Tobacco, Firearms and Explosives, according to a news release.
The agencies served more than a dozen search warrants in the San Gabriel Valley and one in Kansas. Of the 15 wanted individuals, 11 are now in custody, and four remain on the run.
"The indictments, arrests and search warrants executed today - as far away as the state of Kansas - send a message to those directly involved to all those operating criminal enterprises: 'Federal and local police agencies will continue to join and work collaboratively in pursuit of you,'" said El Monte Police Department Chief Jake Fisher.
In a statement, the office of the U.S. Attorney for the Central District of California said the investigation began after a member of the Quiet Village gang murdered El Monte Police Officers Michael Paredes and Joseph Santana on June 14, 2022.
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Santana and Paredes responded to a report of a stabbing last summer at the Siesta Inn, where Justin Flores was found holed up with his wife. The officers rescued the woman, but were subsequently shot to death by Flores, who later fatally shot himself in the head, authorities said.
Days after the officers were slain, El Monte police asked for federal help in going after the leadership of two violent street gangs in the San Gabriel Valley.
According to federal investigators, Flores was a member of one of the street gangs whose leadership was rounded up Wednesday. Members of that gang openly praised Flores for what he did, investigators said. Federal authorities went after the gang leadership like they would any other organized crime group.
"The indictment charges the gangsters with running a criminal enterprise, which engages in various different criminal acts, including murder, attempted murder, witness intimidation, drug trafficking, fraud and illegal gambling," said U.S. Attorney Martin Estrada.
"A highly violent gang responsible for the murders of two brave police officers and others has now felt the weight of a collective law enforcement response," Estrada said. "The gang's days of terrorizing the community stop with today's federal arrests."
Due to the nature of the charges, some of the individuals involved in Wednesday's operation face life in prison or the death penalty if convicted.