A decade on, Walker has sought to appeal his conviction on the grounds that Sullivan had recently claimed sole responsibility for the murder.
His defence argued that if the new evidence was accepted, the Court of Appeal should
substitute Walker's murder conviction with one for causing grievous bodily harm, rather than order a retrial.
In December 2018, Sullivan had arrived at the same prison where Walker had been serving his sentence. The two men had not seen other since their trial.
Sullivan told his therapist he had become "overwhelmed by guilt", according to the Court of Appeal decision given by Justice French.
He claimed he had secretly returned to the scene of the attack alone and delivered the fatal blows.
At a "highly emotional" meeting between the two prisoners - with Corrections in attendance - Walker was reportedly so shocked by the news he became physically sick.
"However, we have come to the very clear view that the evidence is not credible," Justice French said.
"It has all the hallmarks of a story that has been concocted by the two co-offenders."
Both men claimed they had not spoken about it before the meeting.
However, taped phone calls between Walker and others showed that to be "demonstrably untrue", the judge said.
Walker knew all along what Sullivan's story was going to be and that his shock at the joint meeting was "feigned to deceive".
"Mr Walker attempted in evidence to explain away the phone calls but his explanations at times bordered on the absurd," Justice French said.
Furthermore, Walker had raised a suspicion matching Sullivan's claim the day before it emerged to his therapist, according to the decision.
Walker said he had always held this suspicion but had never told anyone - a claim also "totally at odds" with what Walker told his friends after the attack.
The application for leave to cite the further evidence of Sullivan was declined.
