Detectives are to study a tape thought to have been made by child killer Ian Huntley before he attempted to kill himself, police sources said.
The tape - found among Huntley's possessions in Wakefield Prison, Yorkshire - is thought to contain information about the murders of Holly Wells and Jessica Chapman, both 10, in Soham, Cambridgeshire, four years ago.
Sources said the tape would first be examined by West Yorkshire police, who are investigating Huntley's suicide bid, then handed to officers in Cambridgeshire, who investigated the Soham killings.
It would also form part of an internal investigation into Huntley's suicide attempt by prison authorities, sources said.
Huntley, 32, serving life for murdering Holly and Jessica, was found unconscious in his cell at the high security prison in the early hours of Tuesday following a suspected overdose.
Police are investigating the possibility that he gave the tape to a fellow inmate in return for anti-depressant pills.
Neither the Home Office, which runs prisons, nor West Yorkshire Police would comment on the tape. Cambridgeshire Police would only say that officers planned to study the tape.
Holly and Jessica, both 10 and from Soham, vanished after leaving Holly's home to go for a walk in August 2002. Their bodies were found in a ditch two weeks later.
Huntley, a school caretaker in Soham, and his then girlfriend Maxine Carr, a teaching assistant in Holly and Jessica's junior school class, told police that they knew nothing of the circumstances surrounding the girls' disappearance. But it emerged at their trial at the Old Bailey in December 2003 that Huntley had met Holly and Jessica as they walked past his home, enticed them inside and killed them before hiding their remains.
Huntley was given two life terms after being convicted of the girls' murders. Judge Mr Justice Moses later ruled that Huntley must spend at least 40 years behind bars. Carr was jailed after being convicted of perverting the course of justice and has now been released from prison.
