Soham murderer Ian Huntley has died following a prison assault.
The 52-year-old was taken to hospital after being found in a pool of blood following an alleged attack by an unknown inmate on 26 February.
He was attacked in a workshop with a metal bar at HMP Frankland in County Durham.
Police said earlier that a man in his mid-40s was being investigated over the incident.
Huntley was convicted of the murders of 10-year-olds Holly Wells and Jessica Chapman in Soham, Cambridgeshire, in 2002.
He killed them after they left a family barbecue to buy sweets, then dumped their bodies in a ditch.
Huntley was convicted of the murder of both girls in December 2003 and sentenced to two terms of life imprisonment.
Durham Constabulary confirmed that Huntley had died in hospital on Saturday morning.
“Ian Huntley, 52, was taken to hospital with serious injuries following an incident in the workshop on the morning of Thursday, February 26,” a spokesman said.
“A police investigation into the circumstances of the incident is ongoing.
“A file is being prepared for the Crown Prosecution Service for consideration for charges.”
A Ministry of Justice spokesperson said: “The murders of Holly Wells and Jessica Chapman remains one of the most shocking and devastating cases in our nation’s history, and our thoughts are with their families.”
According to The Sun, the attack last month left Huntley blind, and he was not expected to regain consciousness.
The newspaper quoted a source as saying: “Huntley never recovered from the battering and never stood much of a chance of doing so.”
After the attack, the murderer’s only daughter, Samantha Bryan, 27, told The Sun on Sunday that “there’s a special place in hell waiting for him”.
Huntley had been injured in a previous attack at HMP Frankland in 2010, where an inmate slashed his throat with a makeshift knife. The prisoner was jailed for life over the incident.
The crime made Huntley one of Britain’s most reviled killers, with the murder shocking the nation and raising questions about how a man with a history of sexual allegations against him had been allowed to work at a school.
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The best friends were dressed in matching Manchester United shirts when he lured them into his home and killed them.
Their bodies were not found for 13 days, with their disappearance and resulting police search drawing national media attention.
Reporter Brian Farmer, who worked for the Press Association in East Anglia at the time, interviewed Huntley at the time and was so concerned by what he heard he went to the police afterwards.
Farmer was surprised when Huntley began to tell him how he imagined the girls would react to a stranger approaching them, despite not knowing them or working in their school.
The journalist had been trying to interview Maxine Carr, who was a teaching assistant at the girls’ school who was living with Huntley, when the interaction took place.