Brett Rogers, 25, was jailed for a minimum sentence of 32 years last May.
He had been found guilty by a jury of killing his mother Gillian Phillips, 54, and her friend 60-year-old David Oakes in 2015.
Rogers, previously of Stansted Mountfitchet, Essex, was found in his cell at HMP Long Lartin in Worcestershire last Wednesday.
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A post-mortem examination found he died as a result of compression to the neck.
Gary Lindley,  41 and Billy White, 24, have been charged with his murder.
They have been remanded in custody to appear at Worcester Crown Court on Tuesday.
The jury at Rogers' trial was told how he was found at his mother's home in Bentfield Gardens, Stansted Mountfitchet, after the attacks, laughing and covered in blood.
Mrs Phillips had been stabbed at least 41 times in the head, neck and torso. Mr Oakes suffered 56 wounds to his head, face and neck and died of severe head injuries.
A double murderer who killed his mother and her friend has been found strangled in his cell.