Prison guards feared Harold Shipman would continue his killing spree behind bars when he told one inmate: "Remember I am a doctor; I know where to cut you," it emerged today.
The former GP made the threat after he was imprisoned in 2000 for the murders of a string of his patients.
Prison officials warned the serial killer - nicknamed Doctor Death - could kill again after he began 'grooming' inmates in the hospital wing of the high security jail where he was kept for his own protection.
Shipman befriended one wheelchair-bound prisoner at HMP Frankland in Durham, who he pushed around the health centre, and fetched and carried meals for others.
But experts insisted he be banned from contact with all vulnerable inmates for fear it could act as a trigger to further killing, documents revealed today.
A prison dossier seen by the Daily Mail described how staff feared Shipman might "play God" if he saw a prisoner looking frail.
They said he showed a lack of empathy and remorse for any of his victims and was in "total denial" about his crimes.
A 2003 risk assessment from HMP Frankland said: "It is prudent that under no circumstances should Mr Shipman be allowed access in a caring position to any inmate, elderly or not, as this could act as a trigger to further offending."
And in one memo included in the dossier, an unnamed official wrote: "It is my opinion that he presents a considerable risk to some of our more frail/elderly patients.
"My greatest fear is that he witnesses the deterioration in the physical state of either ********** or ********** and decides to 'play God' (we cannot ignore the very nature of his numerous offences)."
Shipman threatened to kill an inmate after he was transferred to Wakefield Prison in West Yorkshire.
A police report filed in February 2004 described how Shipman said: "If you don't shut up, I will kill you - remember I am a doctor, I know where to cut you."
Shipman was jailed for life after being convicted of 15 murders.
An inquiry attributed 218 murders to him but warned he could have killed as many as 250 people.
He committed suicide in January 2004.
A Ministry of Justice spokesman said parts of the dossier of 46 files were revealed under the Freedom of Information Act earlier this month.
He said: "The files cover Harold Shipman's entire term in prison and consequently contain a significant amount of material.
"It was necessary to review all the information in detail to ensure it was suitable for release at this time. Files are being released well ahead of the normal 30 year transfer rule following an ICO ruling.
"Everyone can view the files at The National Archives.
"We will not comment any further on the contents of the files at this stage."