A convicted child killer dubbed the Beast of Wombwell died of natural causes days after he was found guilty of rape and before he could be charged with the murder of another teenager, an inquest has heard.
Peter Pickering, 80, had been locked up for more than 45 years after killing 14-year-old Shirley Boldy in the Barnsley area of South Yorkshire in 1972.
Announcing his death in March, West Yorkshire Police confirmed he was expected to be charged with the murder of another 14-year-old, Elsie Frost, whose body was found in Wakefield in 1965.
Her brother Colin said the family felt they had been "cheated" out of getting justice and believed Pickering could be responsible for other murders.
The sex attacker was also awaiting sentence for raping an 18-year-old woman, who is now in her sixties, a few weeks prior to Shirley's abduction.
An inquest at Reading Town Hall on Monday heard Pickering died at Thornford Park Hospital in Berkshire on March 25, where he had been held since 2014 after being moved from Broadmoor Hospital, also in Berkshire.
The senior coroner for Berkshire Peter Bedford said his family knew of the hearing, but did not want to attend.
"Mr Pickering comes with a history, but the focus of my inquiry is to satisfy myself of the identity of the person who died, where and when the death occurred and how the death came about," he said.
"I will not be going into any history relating to Mr Pickering as it falls outside my inquiry."
He told a handful of reporters and a friend of Elsie's family, who attended the hearing, that Pickering died of natural causes, so a jury was not required at the inquest.
Pathologist Dr Gearoid Kingston, who carried out a post-mortem examination, said he died of a retroperitoneal haemorrhage due to a ruptured abdominal aortic aneurysm.
It also showed he was suffering from heart disease.
The inquest heard Pickering had previously suffered a heart attack in 1996.
Mental health nurse Joshua Muga said he knew Pickering well, having worked at the hospital for two years.
"Mr Pickering had been attending a trial at court and was understandably anxious about this," he said in a statement.
He started complaining of pain to his back, stomach and legs on the evening of March 24, the inquest heard.
Pickering later told Dr Amit Chatterjee he was suffering from "stabbing hot poker-like pain" in his lower back, the coroner said.
He was sitting up in a chair when medics left his room at 11.15pm, but when Mr Muga returned five minutes later he had collapsed on the floor.
Hospital staff and paramedics gave him CPR, but he was pronounced dead at 12.52am on March 25.
A police investigation found nothing suspicious about the death.
Pickering had been held under a hospital order made by a judge in 1972 after he admitted Shirley's manslaughter by diminished responsibility.
She was bundled into Pickering's van as she was returning to Wombwell High School.
Pickering drove her to a secluded location where he tied her up and raped her.
He tried to strangle her before stabbing her to death, a crime witnessed by walkers who were too far away to intervene.
Pickering killed Shirley just three or four weeks after he abducted and violently raped an 18-year-old woman in the Barnsley area.
The victim described Pickering as a "monster" in court and told how he said she was going to die.
Pickering was convicted at Leeds Crown Court on March 20 of rape and false imprisonment over the attack, which only came to light through the reinvestigation of the murder of Elsie.
Elsie was stabbed in the back and head as she walked through a railway tunnel in Wakefield, West Yorkshire, in October 1965.
As part of the inquiry, detectives looked back through Pickering's conversations with psychiatrists and also found a storage garage he rented in the Owlerton area of Sheffield containing possessions including handcuffs and exercise books filled with his rantings.
One note written in 1970 said: "Sex is predominant in my mind - eclipsing all else. Maybe I will be a sex maniac proper. Rape, torture, kill."
Speaking after Pickering's death, Elsie's brother, who pushed for the reinvestigation of the case three years ago along with his sister, Anne Cleave, said: "It's just an incredible feeling of frustration now."
He said the police had done a "fantastic job" but criticised the length of time prosecutors had taken to decide on a charge after detectives handed over the file to the Crown Prosecution Service a year ago.
Mr Frost said: "They uncovered a monster. The man was such a nasty, nasty piece of work."
Asked if he believed Pickering could have killed others, he said: "I think there's every likelihood."
Pickering had convictions for sex offences dating back to the very early 1960s and was in prison from 1966 to early 1972 for a violent sex attack on a teenager.