By Dan Whitcomb

LOS ANGELES (Reuters) - Convicted murderer Gregory Powell, who kidnapped two Los Angeles police officers and killed one of them in 1963, a crime chronicled in the book and film "The Onion Field," has died in prison at the age of 79.

Powell, who was serving a life sentence in prison for the murder of officer Ian Campbell, died of natural causes on Sunday, said California Department of Corrections and Rehabilitation spokesman Lieutenant Andre Gonzales.

Gonzales said Powell died at the California Medical Facility in Vacaville, about 30 miles west of Sacramento, where he had been held since December of 2010.

"The news of Gregory Powell's death is a painful reminder that it was 49 years ago that we lost Officer Ian Campbell," Los Angeles Police Chief Charlie Beck said in a statement.

"In many respects, Officer Campbell's murder in the spring of 1963 has served as a painful reminder of just how dangerous this job truly is day in and day out for all officers."

Campbell's partner on the night of the crime, Karl Hettinger, survived after fleeing in the dark onion field from Powell and his accomplice, Jimmy Lee Smith. Hettinger died in 1994 at the age of 59.

Smith was paroled from a California prison in 1982. He died of a heart attack in a county jail in 2007 after being arrested on a parole violation.

According to an LAPD account of the case, Powell and Smith were looking to commit a robbery on March 9, 1963 when they were pulled over for questioning by Campbell and Hettinger in Hollywood.

Powell and Smith were able to disarm the two officers and drove them to the deserted field in Bakersfield, about 100 miles north of Los Angeles. There Powell shot Campbell dead as Hettinger managed to escape and run some four miles to a farmhouse for help.

Powell was arrested that night and Smith the following day. Both men were convicted of murder and sentenced to death but their sentences were commuted to life in prison when California's death penalty was ruled unconstitutional in the following decade.

The crime became the subject of the book "The Onion Field" by author and former Los Angeles Police sergeant Joseph Wambaugh. The book was adapted into a 1979 film starring James Woods as Powell.

According to the California Department of Corrections and Rehabilitation, Powell had been due for release in 1982, but a parole board ordered him kept in prison amid a public furor.

The corrections department said he was denied parole a total of 11 times and rejected for compassionate release, which he opposed, in October of last year.

(Reporting by Dan Whitcomb; editing by Christopher Wilson)