The cause of death was under investigation, according to the county coroner's office, although foul play was not suspected.
Smith was once sentenced to death for the killing of Officer Ian Campbell, and his parole after 19 years in prison prompted a wave of public outrage when he was released in 1982.
His 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 himself.
Smith, who was on parole when he killed Campbell, spent the last 25 years of his life in and out of prison, usually for drug crimes.
"He was a hype and murderer and we let him out of prison," former Los Angeles Police Chief Daryl Gates told the Los Angeles Times on Saturday. "He should have gone to his death in the gas chamber."
He and Gregory Powell were convicted of abducting Campbell and his partner, Officer Karl Hettinger, from a Hollywood street on March 6, 1963, after the officers stopped
their car for an illegal U-turn. After Powell disarmed the pair by pulling a gun on Campbell and threatening to kill him, he and Smith drove them to an onion field near Bakersfield.
There, Powell shot Campbell in the face. Hettinger bolted, running four miles to the safety of a farmhouse.
Powell was arrested that night and Smith the next day.
The two were originally sentenced to death but the sentences were reduced to life in prison after the California Supreme Court briefly overturned the state's death penalty in the 1970s.
Powell, who remains in prison, has been denied parole several times.
Months after he was paroled in 1982, Smith was returned to prison for failing a drug test.
Paroled again, he was arrested soon after for selling heroin.
In subsequent years he would be arrested again and again on various charges.