"Onion Field" killer Gregory Powell, who abducted a pair of Los Angeles police officers in 1963 and killed one of them, has died in prison.

The state Department of Corrections reports that Powell, 79, died Sunday of natural causes at the California Medical Facility in Vacaville.

The Los Angeles Police Protective League, the union that represents LAPD officers, quickly issued a statement, reacting to the news.

Gregory U. Powell died Sunday after a battle with cancer. He spent almost 50 years in prison for the murder of a Los Angeles police officer.

"LAPD officers have never forgotten the horrific crime committed by Gregory Powell and Jimmy Lee Smith," wrote Tyler Izen, the president of the LAPPL. "Gregory Powell was a cold-blooded murderer who avoided the death penalty, but he won't escape God's judgement."

Powell's death comes on the heels of a memorial to the slain officer, Ian Campbell, whose name graces the Hollywood intersection where the series of events that led to his death began.

Related: Intersection Dedicated to Officer in "Onion Field" Killing

Nearly 50 years ago, Campbell and his then-partner Karl Hettinger were abducted by Powell and Jimmy Lee Smith after detaining the pair during a traffic stop. 

Campbell and Hettinger were on the beat on March 9, 1963, when they stopped the ex-convicts at the Hollywood intersection.

Read original report from NBCLosAngeles.com

After the officers pulled them over, the men pulled out guns and abducted the officers.

Powell shot at Campbell and Hettinger in an isolated onion field near Bakersfield before he and Smith fled. Hettinger, who was not hit, fled to a nearby farmhouse where he got help.

Powell and Smith were arrested that year and eventually convicted of the crime and sentenced to death.

The death sentences were commuted to life in prison after California's death penalty was ruled unconstitutional in 1972.

Over the years, Smith was paroled and repeatedly arrested by the LAPD. He died in 2007 while in prison for a parole violation.

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Powell, who had terminal cancer, was recently denied compassionate release from prison.

Hettinger died in 1994.

Ten years after the killing, Joseph Wambaugh, a former LAPD sergeant, wrote the nonfiction account in a book called "The Onion Field," which also became a movie.

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