(LOS ANGELES) -- A person of interest has been detained in the fatal shooting of a Los Angeles County sheriff's deputy Saturday night, law enforcement sources told ABC News.
Investigators described the murder as an ambush.
Los Angeles County Sheriff's Deputy Ryan Clinkunbroomer was fatally shot after a gray Toyota Corolla pulled up alongside the patrol car he was driving, investigators said.
Clinkunbroomer, who had been on duty, was stopped at a red light outside the Palmdale Sheriff's Station at about 6 p.m. on Saturday.
After the Corolla drove away, Clinkunbroomer's cruiser remained at the light, where a "Good Samaritan discovered him unconscious in his vehicle and promptly alerted Palmdale Station personnel," police said.
Clinkunbroomer, 30, was hospitalized and later died of his injuries, police said.
"This coward of cowards took his life while he waited at a red light," Sheriff Robert Luna said during a press conference.
Homicide investigators with the Sheriff's Department on Sunday asked for information about the Corolla, which they described as a dark-colored sedan with a model year between 2006 and 2012.
It was being sought as a "vehicle of interest" as part of the investigation into the murder of the deputy, according to a special bulletin.
"A widely circulated video from the incident also captured a secondary vehicle traveling alongside Deputy Clinkunbroomer's patrol vehicle, which is of significant interest to our ongoing investigation," the department said in a statement. "We ask for the public assistance locating the vehicle and its occupants."
The bulletin included stills of the vehicle taken from that video, officials said. Homicide investigators found the video as they began "actively conducting interviews, scrutinizing evidence, and reviewing surveillance footage," police said.
Authorities also announced a $250,000 reward for information leading to an arrest and conviction.
ABC News' Amanda M. Morris and Marilyn Heck contributed to this story.
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