Janet Holt claims to have murdered farmer Fred Handford more than 40 years ago - but the body of her business partner, who she says raped her, has never been found.
She admitted the murder to police, but officers believe she is innocent and has ulterior motives for her confession.
And a new ITV documentary, set to be screened tomorrow night (Wednesday), will see Janet speaking to memory expert Jamie Hacker Hughes, to find out if he thinks her claims are credible.
Woman arrested in connection with 30-year mystery of missing man in New MillsSpeaking before her session with Professor Hughes, which will be detailed in the documentary Am I A Murderer?, Janet said: "I’m absolutely certain my memories are true. I’ve no doubt whatsoever. But we’ll see what the expert has to say… I know that’s a possibility that you can have false memories, but I don’t believe that these are.”
In 1976, residents in New Mills were shocked by the sudden disappearance of farmer Fred Hanford. Police carried out a missing person investigation but he was never found, and officers later concluded that he had committed suicide.
But in November 2011, Fred's business partner at Ball Beard Farm, Janet Holt called police and confessed to murdering him. Her claims came after she was treated by a psychotherapist after being plagued by recurring nightmares.
She told detectives that she had been raped by Fred, and concerned that he was do it again, she shot him at point blank range and dumped his body in a shallow grave.
She said: "I thought he was going to do it again. And he had a shotgun and it was leaned against the wall in the corner where I was sat.
"So I picked it up and I pointed it at home and I pulled the trigger. I shot him."
Former duty detective inspector Shaun McElheron realised that there could be something in Janet's claims after she was interviewed by his officers.
He said: “As the evening progressed, the more I got back from the officers, the more I thought there could well be something in this or certainly Janet knows a lot about the case that not many people would have known.”
Police excavated part of the field where Janet claimed to have put Fred’s body - but found nothing.
Janet said: “They took about two foot off the top of the field and then brought me back to show me that there was nothing there.”
Further doubt was cast on Janet’s story after an investigation into her background revealed she was a thief and a convicted fraudster.
Then they discovered that Janet was working with a local journalist, Helen Parker, who was writing her autobiography.
The police believed that Janet had made up her story in order to sell her book.
Helen commented: “When I read it… I did want to know what was causing her nightmares. And I did want to know what had happened to Fred.
"And my initial thoughts were Janet must've been so traumatised by something that had happened with Fred that had caused the nightmares.”
Fred’s daughter Lynette Chapman says she firmly believes Janet murdered him, for monetary reasons: "I’ve read far too many murder mysteries and watched far too many crime thrillers… Who actually benefited the most from it all? And there’s only one person… I think that’s Miss Janet Holt.
“If he'd committed suicide, surely some remains would have been discovered at some point because I don't really think it's your priority when your committing suicide to hide your body. So, unless you're in some really obscure place I can't see how a body can be hidden.”
Am I A Murderer? will be screen on ITV at 9pm on Wednesday October 10.