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.

Cleveland Police used anti-terror powers as part of an investigation into alleged leaking of confidential material to newspapers in 2012.
However, the force claimed it was justified in secretly monitoring the phones of two former officers.
Mark Dias and Steve Matthews claim they were targeted after challenging misconduct by fellow officers.
The decision over whether the force's covert techniques used against its former employees were lawful will be made in the new year, following an Investigatory Powers Tribunal.
At the hearing in London, Judge Sir Michael Burton said although he reserved judgement until 2017, it was clear what his decision would be.
He said the force should start thinking about compensation for the two officers.
Cleveland Police claimed it was justified in using the Regulation of Investigatory Powers Act (RIPA) - which has since been replaced.
In a four-month period the force monitored over a million minutes of telephone data, the tribunal heard.
Mr Matthews, the former head of Cleveland's Police Federation, said: "I honestly think they were trying to stitch me up."
If anyone criticised the force "they would be jumped on and, as part of that campaign, I was singled out", he said.
Mr Dias said the force monitored his phone calls, emails and activity.
The officers' legal team said the "force's casual disregard for the legal framework beggared belief".

Dyfed-Powys Police said its officers made arrests relating to controlled drugs at the dance party near Llanddewi Brefi over the bank holiday weekend.
Local people and councillors have called for action to ensure more raves are not held.
Organisers of the event had relayed the remote location to people via text and email rather than social media.
Police said they became aware of a "large gathering" late on Saturday, 28 May but because it was already on a  "a very large scale" the decision was made not to break up the party.
Instead, officers stayed at the event to ensure more people could not enter the site.
The police helicopter helped to gather intelligence and evidence and arrests were made.
Llanddewi Brefi councillor Rhodri Evans said: "I have had quite a few people in Llandewi expressing their concerns - people driving through the village at very high speeds and perhaps putting people in danger."
He added that the area was "quiet and peaceful" and villagers wanted to ensure more raves were not held.
Officers have urged landowners to be vigilant to people enquiring about their land in the guise of hiring it for apparently acceptable activities such as gymkhanas and scouts and guides events.
A double murderer who killed his mother and her friend has been found strangled in his cell.
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A police force has admitted to unlawfully accessing the private phone records of journalists and a solicitor.
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Police are investigating after about 2,000 people turned up for a three-day illegal rave in Ceredigion.