Huntley’s life support was switched off on Friday, the BBC understands.
The brutality of his crimes made him a target in prison and he had been attacked several times previously. The BBC understands that triple killer Anthony Russell, 43, is suspected of attacking Huntley.
Sources previously told the BBC Huntley was found lying in a pool of blood after being bludgeoned with a makeshift weapon at a workshop at the high security prison in County Durham.
Durham Constabulary have said they are preparing a file for the Crown Prosecution Service for the consideration of charges.
A spokesperson for the force said “a police investigation into the circumstances of the incident is ongoing”.
Holly and Jessica vanished after leaving a family barbecue in their small town near Cambridge in August 2002.
It is believed they were on their way to buy sweets when Huntley, then aged 28, lured them back to his home and killed them.