An accomplice of the so-called Freeway Killer who terrorized Southern California 36 years ago has been killed in prison, officials said Thursday.

Gregory Miley, 54, was attacked by another inmate in a Mule Creek State Prison exercise yard Monday evening, said state corrections department spokesman Joe Orlando.

He was sent back to his cell after an examination at the prison's medical facility, but became unconscious about 90 minutes later. Orlando said Miley died at an outside hospital Wednesday afternoon after he was taken off life support.

The state inspector general issued a scathing report last week saying Mule Creek provides poor medical care to inmates.

Miley was serving two life sentences for assisting "Freeway Killer" William George Bonin. Bonin was executed in 1996, the first in California to die by lethal injection.

Miley's convictions in Los Angeles County in 1982 and Orange County in 1983 were for killing two boys, ages 14 and 12.

Bonin was sentenced to die for killing 14 young men and boys from 1979 to 1980 and dumping their naked bodies along freeways.

The victims, ages 12 to 19, were sexually abused, tortured and all but one was strangled. That victim, a 17-year-old German tourist, was stabbed about 70 times. One victim was found with an ice pick in his head, while others had been burned with cigarettes.

Bonin received two death sentences, but was convicted of 10 murders in Los Angeles County and four more in Orange County. He once told a television reporter he had killed 21 people.

Miley and another accomplice, James Munro, testified against Bonin in exchange for lighter sentences. Another suspected accomplice hanged himself before trial.

Orlando couldn't say if Miley's crimes were believed to be a motive for the assault or why he was attacked.

"It's an ongoing investigation so we can't say very much," Orlando said.

He wouldn't say if a weapon was used or give details on the other inmate.

Mule Creek houses about 3,000 inmates in Ione, about 40 miles southeast of Sacramento.