Kenneth Peatfield, 50, of Sheffield, was found guilty of murdering his partner Susan Craven, 54, whom he planned to replace with his teenage lover.
Mrs Craven's head, which was probably cut off with a power saw, was found in a two-feet block of concrete at the house she shared with Peatfield. The rest of the dead woman's remains have never been found.
The nine women and three men on the jury at Sheffield Crown Court gasped when they learned after giving yesterday's verdict that Peatfield had earlier been convicted of trying to kill his wife and 10-year-old daughter. He was jailed for 10 years in 1984 for hiring a hit-man to murder his wife Janet and daughter Helen.
He had planned to inherit pounds 50,000 through an insurance policy, but the plot back-fired when the hit-man refused to carry out the killings and went to police. His ex-wife Janet, now 50, said at the time of the trial: "He was a good husband and father and I was so shocked that he could do such a thing."
In his defence in this latest case, Peatfield claimed that someone had swapped the concrete block containing his wife's head with one he had made as part of a garden ornament.
Jailing him for life yesterday, Mr Justice Bell said: "You murdered the woman with whom you had lived for some years. A woman who needed your support. You murdered her when you were infatuated with a much younger woman who you hoped would come to live with you in Susan Craven's place."
Peatfield did not react as the verdict was announced at Sheffield Crown Court, but relatives of Mrs Craven sighed with relief.
The jury was told that Mrs Craven disappeared on 5 March last year. Two days later, Peatfield took his lover, Faith Warner, 17, to the home and told her: "I'm going to show you something now that is going to change your life."
Michael Murphy QC, prosecuting, said Peatfield led Miss Warner into a brick outhouse, showed her the body of Mrs Craven under a blue tarpaulin sheet, and said: "I did it so I could be with you."
Miss Warner, now 18, of Ashton, Greater Manchester, said Peatfield threatened her after showing her the body.
"He grabbed both of my arms and he went blood-red, literally, and he shook me and said: `If you tell anybody I will kill you and I will kill your family'."
She was 17 when she started going out with Peatfield and became pregnant with his baby in 1987. "He was very lively, he made me laugh, he was quite a bubbly person. I wasn't bothered about the age difference, although he was worried I would trade him in for a younger model," she said.
Peatfield told a series of lies to friends and neighbours, saying Mrs Craven had left him after an argument. But they did not believe him and eventually reported Mrs Craven missing.
It was not until 20 April, the day after Peatfield was charged with the murder, that detectives examined the block of concrete. Forensic scientists found spots of blood in the dining room, on the carpet and on the curtains of the couple's home.
Peatfield, a consultant engineer, who stood to gain more than pounds 200,000 from Mrs Craven's death, denied having murdered her. He said they had a great relationship and never argued.Reuse content