Updated

A Los Angeles County police officer was found shot to death Wednesday night in the parking lot of police headquarters in Downey, prompting authorities to conduct a massive manhunt for suspects.

Three males, including a juvenile, were in custody after a massive manhunt for the suspects, initially described by police to be two males. Authorities first said the officer-- who was identified as Ricardo Galvez-- was likely targeted, but changed the theory to a botched robbery attempt at an afternoon press conference. Authorities do not believe Galvez was targeted.

"He never saw them coming," Los Angeles County Sheriff Lt. John Corina said. "He never had a chance."

Galvez, who was a police officer for the department for five years. He was a U.S. Marine who served two tours in Operation Enduring Freedom.

The shooting occurred at about 11 p.m. in the west side of the parking lot. Galvez was in the driver's side seat of his unmarked car nearing the end of his shift. Two suspects approached the unmarked vehicle and at some point fired into the car, authorities said. Another patrol car happened to be driving in the area and heard the shots, pursued the suspects and chased them into the city of Montebello. SWAT teams searched buildings in the city.

"Words cannot express the love and respect we have for Ricky," Carl D. Charles, the Downey police chief, said at a press conference Thursday morning. "Our department is hurting."

Fox News' Edmund DeMarche and The Associated Press contributed to this report