Roberto Sanchez, a six-year veteran, died at a hospital after the patrol car he was driving was broadsided by an SUV in the Harbor City area. The squad car was so mangled that Sanchez's partner had to call for help on his personal cellphone because the police radio wasn't working.
LAPD Chief Charlie Beck said Sanchez was on patrol with his best friend when the collision occurred.
The surviving officer, whose name was not released, was hospitalized with a broken jaw and other injuries.
Sanchez was the third LAPD officer to die on the job recently. In March, 40-year-old Officer Nicholas Choung Lee was killed when his patrol car was hit by a dump truck in Beverly Hills. Last month, 51-year-old motorcycle officer Chris Cortijo was struck and killed by a driver alleged to have been under the influence of cocaine.
Mayor Eric Garcetti ordered city flags lowered to half-staff.
"This third loss of an officer in the line of duty in just two months is a stark and tragic reminder of the dangers our first responders face every day," Garcetti said in a statement.
The Los Angeles police union called Sanchez a hero.
"Today the world has lost a true hero. Roberto will be greatly missed as a protector of our society and even more as a person," Los Angeles Police Protective League President Tyler Izen said in a statement.
Investigators were piecing together the accident. Preliminary information from the crash site suggested the officers were following another car when both vehicles made a U-turn. The SUV then slammed into the patrol car, police said.
The SUV driver fled the scene, and police later detained a person of interest. No other details were available.