"We will always bring to justice anybody who would not only murder a police officer but anybody who would take the life of any Angeleno," Garcetti said. Francisco Talamantes, 23; Cristian Facundo, 20 and Ashlynn Smith,18, all of Temecula, were booked on suspicion of murder and held without bail, police said.
It wasn't immediately clear whether they had obtained lawyers. Police also did not immediately specify each person's role in the shooting. "Although this investigation is ongoing, which limits our ability to provide further details at this time, we feel confident a murderer is off the streets," the police department said in a post on Twitter .
Diaz, 24, is the second off-duty officer killed in the Los Angeles area in recent months. In June, Los Angeles County Sheriff's Deputy Joseph Gilbert Solano was shot and killed at a Jack in the Box restaurant in the eastern Los Angeles suburb of Alhambra.
The suspect, Rhett Nelson of Utah, is also charged in the killing of professional Russian snowboarder Dmitry Kolstov. Authorities have said that the killings of Solano and Kolstov are believed to be random. Nelson has pleaded not guilty in both cases.
Diaz on Saturday was standing in line at a taco stand in the Lincoln Heights neighborhood at 1 a.m. with his girlfriend and two other males when he noticed a man vandalizing something nearby and approached him.
The man, who authorities believe is a member of the Avenues gang, left but returned a short time later with a group of other males and lifted up his shirt to display a handgun. Diaz and the others tried to get into a car to avoid violence, but the man started shooting, police have said. The officer and one of the other males were hit by gunfire. Diaz died from his wounds and the other man was hospitalized.
"Today's and this morning's operations represents significant steps on the road to justice for Juan Diaz, the others who were with him that night and his entire family," Assistant Police Chief Beatrice Girmala said.
Diaz had been on the force for two years and was assigned to the police department's Professional Standards Bureau. "Through due diligence and a penchant for justice, we have moved one step closer to bringing justice to fallen LAPD Officer Juan Diaz and his family," Chief Michel Moore said in a post on Twitter . "We continue to offer prayers and condolences to his family during this unimaginably difficult time."
The union that represents Los Angeles Police Department officers said prosecutors should seek the death penalty in the case. "We are grateful that the cowards and thugs accused of the cold-blooded murder of Officer Juan Diaz are in custody," the Los Angeles Police Protective League said in a statement.
California Gov. Gavin Newsom, a Democrat, issued a moratorium on death row executions in March that granted temporary reprieves to more than 700 inmates. He said no executions would take place during his term. California has executed 13 inmates since the U.S. Supreme Court reinstated the death penalty in 1976.