Mitchell is believed to be planning to sue Nigel Beaumont for “negligence and misrepresentation” at his trial for brutally murdering his 14-year-old girlfriend Jodi Jones.
An insider at Shotts Prison in Lanarkshire, where the 22-year-old is serving a life sentence, said “deluded” Mitchell has already spoken to a lawyer about launching a private prosecution against Mr Beaumont.
The source said: “Mitchell has spoken to a lawyer about suing Nigel Beaumont on the basis that he failed in his job.
“As far as Mitchell is concerned, it is Beaumont’s fault he’s behind bars.
“Mitchell is determined to clear his name and will stop at nothing.
“He is deluded.
“He genuinely believes he has a strong case.”
Mitchell was 14 when he carried out the attack on Jodi; whose body was found mutilated and bound in woodland near her home in Dalkeith, Midlothian, in 2003.
He was convicted of murder at the High Court in Edinburgh in 2005 and will serve a minimum of 20 years behind bars.
Previous appeals to have his conviction quashed and sentence reduced have failed.
At the trial, Mitchell claimed his dog had found Jodi’s body because it recognised her scent, but prosecutors argued he had known all along where her body lay.
Mitchell, also from Dalkeith, claims Mr Beaumont should have gathered evidence to back-up his claims.
Mr Beaumont, who built the defence case, led by Donald Findlay QC, said: “Mr Mitchell’s case was conducted with the utmost maximum care.
“All possible avenues were investigated in terms of the evidence led.
“I refute and suggestion that myself, or any other member of Mr Mitchell’s defence team, were negligent.”