The younger man said he was not sorry for what happened "and it was simply a task to be carried out for the gang".
Nuku believed Roper was pretending to be a Mongrel Mob member when he was actually affiliated with Black Power.
Lake initially attacked Roper, a flurry of punches leaving him on the ground. Nuku instructed him to break the murderer's arm but Lake struggled to do so.
Frustrated with how long it was taking, Nuku jumped in, kicking Roper and putting him in an arm lock which eventually snapped the bone.
He tried to break the victim's other arm and both his legs but was unsuccessful.
Lake then punched him in the head several times as Roper lay there nursing his broken limb.
But the 32-year-old was not finished.
"You then jumped at least a half metre in the air and landed with both feet on the victim's head," Justice Mark Woolford said.
"This move you repeated three times."
Roper was left semi-conscious with a broken arm, a fractured jaw and a fractured skull.
The attacker offered no reason for the stomping.
Realising Corrections officers were not coming, Lake put Roper in the recovery position and sounded an alarm.
The court today heard how Nuku had been jailed most recently for burglary but had the sentence increased last year when he attacked another inmate during a dispute over nicotine.
Lake is serving a six-and-a-half-year stint for wounding with intent to cause grievous bodily harm.
Roper was found guilty of killing Ms Tovizi after a High Court trial by either putting her in a sleeper hold or holding her head under water.
He then took her car and laptop, withdrew money from her bank account, and told family she had "done a runner".
He challenged his murder conviction but the Court of Appeal rejected all of his points.
