Photo: KTLA

Two suburban Los Angeles police officers thought they were helping a driver after a car crash.

Then, authorities say, he pulled a gun.

Whittier Officers Keith Lane Boyer and Patrick Hazell didn't know that the motorist allegedly had killed his cousin hours earlier in neighbouring East Los Angeles and stolen his car.

"They walked up on the vehicle believing the motorist was in need of medical help and then they ended up in a gunfight for their lives," Los Angeles County Sheriff Jim McDonnell said.

Monday's morning's shootout killed Boyer. It left Hazell and the suspected gunman hospitalized and Whittier in shock.

Boyer was "the best of the best," Police Chief Jeff Piper said at an afternoon news conference. He wept as he described his friend of more than 25 years.

"All of us have been grieving," the chief said. "And I didn't think I had any tears left."

The officers answered the report of a car accident at about 8:30 a.m. and a driver pointed them to the vehicle which had rear-ended his car, police said.

That driver had gotten out and asked those he had hit to help push his stolen car from the intersection, investigators said.

The officers approached the motorist, a 26-year-old gang member with a history of serious offences who had been granted early release from jail about a week ago, county sheriff's Lt. John Corina said.

"When they get him out of the car, they go to pat him down for weapons, they can see he's got tattoos all over his face and all over his neck," Corina said.

The man then pulled a semi-automatic handgun from his waistband and opened fire at the officers, who were wearing bulletproof vests and shot back, Corina said.

Boyer was pronounced dead at a hospital. Hazell and the alleged gunman, whose name wasn't immediately released, were hospitalized in stable condition and were expected to live, authorities said.