Police said: “Emergency services were called to reports of an assault in the workshop on the morning of Thursday, February 26.”
Huntley, 52, was taken to hospital with serious injuries where he died nine days later, police added.
He had been serving a life sentence, with a minimum term of 40 years, for murdering the schoolgirls.
The Ministry of Justice has previously said Huntley’s crime “remains one of the most shocking and devastating cases in our nation’s history, and our thoughts are with their families”.
