A child killer dubbed the "Beast of Wombwell" died after having a heart attack at a secure psychiatric unit, an inquest has heard.
Peter Pickering, 80, stabbed and strangled Shirley Boldy, 14, in Wombwell, near Barnsley, in 1972.
He was also suspected of murdering schoolgirl Elsie Frost in 1965.
An inquest at Reading Town Hall heard Pickering died at Thornford Park Hospital in Berkshire after complaining of back and stomach pain.
Senior coroner Peter Bedford said: "The reports currently available show he was feeling unwell on 25 March, and was reviewed by a doctor, who asked for a urine sample.
"He was left alone for no more than five minutes before a nurse returned to find him collapsed on the floor, clearly in pain."
An ambulance was called, and despite CPR being administered, he died at the scene, Mr Bedford said.
The coroner said a post-mortem examination found Pickering died from a retroperitoneal haemorrhage due to a ruptured abdominal aortic aneurysm. It also showed he was suffering from heart disease.
He adjourned the full inquest until 18 June.
In March, Pickering was convicted of raping a woman weeks before he killed Shirley and was waiting to be sentenced.
Pickering was convicted of rape and false imprisonment over the attack, which only came to light through the re-investigation of the murder of Elsie Frost.
After his death, West Yorkshire Police said it had expected to charge the convicted killer with the murder of Elsie Frost in Wakefield in 1965.
"His unexpected death clearly means that will no longer happen," Det Sup Nick Wallen said.
As part of the inquiry, detectives found a storage garage Pickering rented in 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."
After his death, members of Elsie's family - who had pushed for the case to be re-investigated - said there was "just an incredible feeling of frustration now".