The Prison Service is to review how all phone calls to Soham murderer Ian Huntley are recorded after a newspaper published comments he apparently made.
Ian Huntley murdered Holly Wells and Jessica Chapman
The Sun claims Huntley admitted lying in court, purportedly saying that schoolgirl Jessica Chapman died in his living room, not bathroom.
The Sun has refused to reveal the origins of the tape.
The Prison Service says the recording was probably made during a conversation between Huntley and a relative.
The killer has always maintained Holly Wells died accidentally in the bath and Jessica was inadvertently killed, also in the bathroom, as he tried to silence her screams.
A spokesman for the Prison Service said: "There was no evidence that Huntley was interviewed by The Sun.
"It does appear to be a taped discussion between Huntley and a close family member."
There would be a review into the way Huntley's calls were recorded by the service, he added.
Cambridgeshire Police said Huntley's comments simply added to the confusion surrounding the truth of what happened.
"All we want and all the families want is the truth.
"So far all we've had is several different versions of events from Huntley - this just causes more and more pain for Holly and Jessica's parents.
"We still hold out the hope that Huntley will speak honestly at some stage and that the first people to know about that should be Holly and Jessica's parents."
Huntley was jailed for life for murdering the 10-year-olds after an Old Bailey trial last year.
Speaking from Wakefield prison, Huntley reportedly said: "I said that Jessica died in the bathroom. She didn't.
"She died in the living room. Everything happened as I said it did, apart from that.
"As soon as I got Holly out of the bath and everything, and realised she was dead, Jessica just went schiz."
Huntley said he had taken Jessica to the living room, and she had tried to leave, the Sun said.
According to a transcript of the tape published in the Sun, he added: "I don't know what was going through my head. I certainly don't recall thinking, 'I've got to kill her to stop her leaving'.
"I think it was my intention just to stop her."
Huntley reportedly admitted switching off Jessica's mobile in the bathroom because she was trying to call someone.
He also claimed he was threatening to go on hunger strike in two weeks time in an attempt to kill himself, said the Sun.