By Linda Deutsch

LOS ANGELES (AP) -- Gregory Powell, who was convicted of killing a Los Angeles police officer during an infamous kidnapping that inspired Joseph Wambaugh's true-life crime book ``The Onion Field,'' has died in prison at age 79, the California Department of Corrections and Rehabilitation said Monday.

Greogry Powell — Gregory Powell (California Department of Corrections and Rehabilitation)

Powell died late Sunday in a hospice at the California Medical Facility, a men's prison in the Northern California city of Vacaville.

Powell, who spent close to a half century behind bars, was denied parole last year when he told a parole board he was suffering from prostate cancer and wanted to spend his last days outside prison.

``I've done enough time. I'm a different man, and I'm ready to be paroled,'' he was quoted as telling the parole panel members who were unmoved.

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``It was a cold, deliberate crime, and he had a long time to reflect on it,'' said Los Angeles Deputy District Attorney Alexis De la Garza, who argued at the hearing for Powell's continued incarceration.

Powell and a co-defendant, Jimmy Lee Smith, were convicted of abducting Officer Ian Campbell and his partner Officer Karl Hettinger from a Hollywood street on March 6, 1963, after the officers stopped their car for making an illegal U-turn.

Powell disarmed the officers by pulling a gun on Campbell and threatening to kill him. Then he and Smith drove them to an onion field near Bakersfield.

Wrongly believing they had violated the federal kidnapping statute known as the ``Lindberg Law,'' and faced the death penalty if captured, Powell shot Campbell in the face.

Hettinger bolted as Powell fired at him. He ran four miles to the safety of a farmhouse.

Powell and Smith, both ex-convicts, were arrested soon after.

Hettinger was haunted by the events of that night for the rest of his life and was shunned by his colleagues. He left the force and went into the nursery business and became a Kern County supervisor. He died in 1994 at age 59.

Powell and Smith were originally sentenced to death but the sentences were reduced to life in prison when the California Supreme Court overturned the state's death penalty. The punishment has since been reinstated, but didn't apply retroactively.

The crimes were documented in 1973's ``The Onion Field'' and the 1979 film of the same name, both written by Wambaugh, a former Los Angeles police officer.

Wambaugh said in a 2011 interview with The Associated Press that he visited Powell and Smith in prison when he was writing the book and found that they were fairly intelligent men whose lack of violent histories made their crime inexplicable.

``They were both smart guys and just petty criminals who got in over their heads one night,'' Wambaugh said. ``Who would have thought two such losers would do such a horrific crime?''

He said when he asked Powell if he had any complaints about the manuscript for ``The Onion Field,'' he had only one.

``He said, `I don't think I'm nearly as physically unattractive as you seem to think I am'' said Wambaugh. ``That hurt his vanity.''

Powell tried 11 times for parole. The Los Angeles police union opposed his release even when he said he was terminally ill. Campbell's daughter appeared at the last parole hearing and said it would be an insult to all police officers if Powell was released.

Wambaugh said that one of Powell's lawyers often complained that ``Powell would have been out of prison if it hadn't been for `The Onion Field' book. And I think he was right. The book kept Powell in prison. It just became so famous.''

Asked how he felt about that, Wambaugh said, ``I'm not shedding any tears.''

Smith, who was depicted in the book as a follower, was paroled in 1982. He was subsequently arrested numerous times, mostly on drug-related charges.

He died April 7, 2007, of a heart attack at the Pitchess Detention Center in Castaic, where he was being held for failing to report to a parole officer.

Karl HettingerKarl Hettinger

'Onion Field' Killer Dies in California Prison