For more than three decades, Edna Worley struggled to cope with the rape and murder of her teenage daughter.

Her comfort: that killer John Errol Ferguson would be executed for killing Belinda Worley, 17, and seven others.

Worley, however, died in May.

“She always said Ferguson would outlive her and if she could, she would pull the switch,” said her son, Michael Worley, 49, of Cooper City. “She waited for the execution her entire life right up to her death.

“She kept every newspaper article and would visit Belinda’s grave every week right up to the week she died. She planned on attending the execution. She wanted to be there for her daughter when Ferguson was executed.”

After nearly 35 years of appeals, Ferguson is scheduled to die Thursday by lethal injection for a 1970s murder spree that shocked South Florida.

His supporters, however, say his execution is “cruel and unusual punishment” because his severely ill mind long ago succumbed to delusions and hallucinations, including regular communication with his dead father.

“Nationally-recognized experts in neuropsychiatry and forensic psychology examined John and testified that he lacks a rational understanding of why he is being put to death,’’ said his lawyer, Christopher Handman.

Ferguson, on Death Row since 1978, is unfamiliar to newer generations. He was convicted of murdering six inside a Carol City house — then, the largest mass murder in Dade history.

He also shot and killed Belinda’s boyfriend, Brian Glenfeldt, 17, whom she met through a Hialeah High Christian youth group.

Ferguson also was convicted of attempted murder in the robbery of another couple at a lover’s lane. Detectives suspected, but never charged him with, the brutal robbery-slaying of an elderly couple at a Miami motel.

“He was a pretty vicious man,” said retired Miami-Dade Judge Robert Kaye, who as a prosecutor in 1978 put Ferguson on Death Row. “We had pretty good information that he killed at least 12 people.”

Defense attorneys say Ferguson grew up the son of an alcoholic, abusive father. His mother abandoned him at age 11, leaving him in a house overrun with snakes, scorpions and chickens.

When Ferguson was 21 years old, he stole a deputy’s gun and was about to shoot when the deputy fished another gun from his boot, shooting Ferguson four times — including a round to the head.

“After returning from the hospital, he began to show serious mental instability, irrational thinking, unexplainable hostility and grossly impaired intelligence,” according to a biography prepared by Ferguson’s lawyers. “As time passed, these conditions worsened.”

He spent several years in state psychiatric care. One doctor called him “homicidal” and said he “should not be released under any circumstances.”

Ferguson was nevertheless discharged from a state hospital, convicted of robbery and sent to prison, where he served 225 days.

In May 1977, police found an elderly couple from St. Petersburg — in town for a funeral — shot to death at Miami’s Gold Dust motel. The couple had been tied up, robbed, brutally beaten and shot, execution-style.

The same handgun was used to slay the “Carol City Six” in July 1977.

Ferguson and three others, posing as electrical workers, tied up eight people, shooting each in the head.