A pensioner dubbed the Beast of Wombwell has died just days after being convicted of raping an 18-year-old woman before he raped and killed a 14-year-old girl more than 45 years ago.
Peter Pickering, 80, died on Saturday night after being taken ill in secure psychiatric accommodation in Berkshire, West Yorkshire Police said.
The force also revealed that Pickering was the man arrested and interviewed over the past two years in the murder investigation of Wakefield schoolgirl Elsie Frost, who was killed in 1965.
Detective Superintendent Nick Wallen, of West Yorkshire Police, said: "We can now formally confirm that Peter Pickering was the man we arrested and interviewed over the last two years as part of the renewed investigation into the murder of 14-year-old schoolgirl Elsie Frost in Wakefield in 1965.
"We strongly suspected that Peter Pickering was responsible for her murder. We had been liaising with the Crown Prosecution Service and it was our expectation that Pickering would be charged in due course.
"His unexpected death clearly means that will no longer happen. We have informed all those involved in the case of this development and we will be liaising with the West Yorkshire Coroner as to what proceedings are now necessary in relation to Elsie Frost's death."
Elsie was attacked from behind and stabbed in the back and head as she walked through a railway tunnel just off a canal towpath.
A major inquiry was launched after her body was found at the bottom of a flight of steps by a dog walker.
In 2015 police launched a fresh appeal to find her killer.
In the wake of the appeal Elsie's brother, Colin Frost, spoke out about her family's pain, saying that their parents, Edith and Arthur, had died "with a huge amount of guilt".
In 1972 Pickering was subjected to a hospital order without limit of time for the manslaughter of Shirley Boldy by reason of diminished responsibility.
He has never been released and was being held at Thornford Park Hospital, in Berkshire.
Leeds Crown Court heard how Shirley was 14 when she was abducted, raped and killed by the sex attacker in Wombwell, near Barnsley.
A woman, who is now in her 60s, told a jury how she was assaulted by Pickering just a few weeks before Shirley's death.
On Tuesday, Pickering, who appeared at court via video link from Swindon Crown Court, in Wiltshire, and denied rape and false imprisonment, was found guilty by the jury after two hours of deliberations.
Giving evidence, the woman described how she was picked up by the defendant who took her to a secluded spot and cut off her underwear with a knife, handcuffed her, raped her, burned her breasts with cigarettes and told her she was going to be killed.
The woman told the jury: "I remain of the fervent belief that whether he has a mental illness or not the man is a monster and wherever he is now that's the right place for him to be."