A California man once known as the nation's worst serial killer was denied parole again for murdering and mutilating more than two-dozen farmworkers 45 years ago, officials said Thursday.

Juan Vallejo Corona, 82, was denied parole for another five years and will keep serving his life sentence in Corcoran State Prison, corrections department spokesman Luis Patino said.

Corona, a farm labor contractor with a history of mental illness, was convicted of killing and mutilating 25 men with a meat cleaver, machete, double-bladed ax and wooden club that investigators found in his home, all stained with blood. The bodies were found all at once, but he said in 2011 that the slayings occurred over a year.

It was the nation's deadliest rampage until John Wayne Gacy Jr. was convicted in 1980 of killing 33 young men and boys in Chicago. Gacy was executed in 1994 in Illinois.

Corona was convicted of stabbing 24 of the men, hacking open their heads and burying their remains on two ranches where he once worked near Yuba City, 40 miles north of Sacramento.

"It was a gruesome manner of killing. He hacked these people to death," said Sutter County District Attorney Amanda Hopper, who attended Wednesday's hearing to argue against Corona's release.

He shot the 25th victim in the head, something he could do again if he were released from prison despite his age and use of a wheelchair, Hopper said.

Investigators found a ledger book at Corona's home containing the names of seven victims. Four of the bodies have never been identified, and the remains of 14 victims were never claimed by family members after they were discovered in 1971.

Prosecutors previously said Corona sought victims who had few relatives and likely would not be missed. No family members of his victims attended the hearing.

Corona, a Mexican national and native of Jalisco, Mexico, acknowledged his guilt for the first time during a 2011 parole hearing, prosecutors said at the time. He justified the killings because he said the men were "winos" who were trespassing in the orchards north of Sacramento.

But he backtracked this time.

"When it had anything to do with killing the 25 people or his mental state, he conveniently could no longer remember," Hopper said of Corona's comments at this week's hearing. "He specifically said that, 'I don't remember that I killed anyone, I don't remember that I did anything.'"

However, Corona was otherwise lucid despite being previously diagnosed with dementia and mental illness, the prosecutor said.

Corona was first convicted in 1973 of 25 counts of first-degree murder. It was overturned on appeal, but he was convicted again in 1982 and sentenced to 25 years to life in prison. He was not eligible for the death penalty because California's capital punishment law had been ruled unconstitutional at the time.

This is the eighth time he has been denied parole.