Viktor Dembovskis was serving three life sentences for the rape and murder of 17-year-old Jeshma Raithatha in Greenford, west London, in 2005.
Latvian national Dembovskis, 63, died on December 20 at HMP Frankland in Durham.
He was one of five inmates at the prison to die in the space of eight days last month.
Investigations into each of their deaths are underway, with Prisons and Probation Ombudsman (PPO) Adrian Usher saying he will look at any “themes or any correlation among the deaths”.
However, the Northern Echo said it is understood that the five deaths are not directly linked.
Dembovskis waited in a “den” along a footpath and attacked Jeshma as she walked home from school days before her 18th birthday.
Her body was discovered eight days later.
Dembovskis fled the country after realising he had left his keys at the murder scene but was extradited back to the UK.
His sentence meant he would never have been eligible for release from prison.
His death is under investigation by the PPO and an inquest will be opened in the coming weeks.
