Peter Pickering, who was found guilty of raping a teenager and killing another minor girl almost 40 years ago, had managed to successfully escape the UK justice system for the murder of 14-year-old Elsie Frost in Wakefield in 1965.

Pickering allegedly stabbed Elsie Frost to death and escaped justice before he went on to kill 14-year-old Shirley Boldy in Wombwell, Barnsley, several years later in 1972. He was even dubbed the "Beast of Wombwell" for his crimes. He was also accused of sexually assaulting two other minor girls.

The hunt for Elsie Frost's killer had made national headlines and had even led to the questioning of 12,000 people by the police. He was also one of the likely suspects, but the police ended up ruling him out at the time.

The alleged evidence of his crimes were found in two secret lock-ups which Pickering kept in Sheffield and Liverpool. The lock-ups had letters that he had written to his girlfriends, along with diaries, handcuffs and women's underwear.

"You have caused me to do what I'm about to do – you watch what happens next!" read one of the letters he had written to a girlfriend.

"...I will surely go down in flames this time...I shall have to take someone with me when I go. So now what? To join the I'm really going to get good and bloody nasty. Thanks to you," he added.

One of the letters that he had written to his mother indicated that he had also raped an 18-year-old woman weeks before killing Boldy in 1972.

According to a report in Yorkshire Live, West Yorkshire Police was about to charge Pickering with Elsie's murder when he passed away in 2018.

"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," West Yorkshire Police had said then.

Elsie Frost's case was reopened in 2015 after her sister got in touch with the BBC to speak about the case and to seek justice. Radio 4 had then run a series called "Who Killed Elsie Frost?"

"Pickering's name had already cropped up because a file was sent up from Scotland Yard," said Frost's sister Anne Cleave.

She continued: "The outcome of that, of course, is the fact that Pickering goes on to commit other crimes. If things had gone as they should have done in 1965, those events may not have happened and maybe then my sister's case would have come to full fruition." Pickering died of a heart attack in March 2018.

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Crime scene police line | Representational Image Photo: GETTY IMAGES / SCOTT OLSON