Notorious murderer John Walsh wanted his cellmate "gotten rid of" so he bashed him at least eight times in the head with a sandwich press, a Sydney court has heard.
The 79-year-old has pleaded guilty to murdering fellow convicted killer Frank Townsend, who died from his injuries after the Long Bay prison cell attack on January 2 in 2017.
At his sentence hearing in the NSW Supreme Court on Friday, crown prosecutor Sharon Harris said Walsh's first "cold rage" beating with the Breville metal sandwich iron was interrupted by prison guards.
But he struck twice more when the officers left thinking Townsend was just making "snoring" noises, and saw Walsh seated on his own cell bed, she said.
"Your honour, some people are just bad," Ms Harris said to Justice Lucy McCallum.
"The offender himself refers to himself as a dangerous person, or implies that he's a dangerous person."
In his police record of interview, Walsh made derogatory comments about Townsend and referred to "having gotten rid of" him, the crown prosecutor said.
Ms Harris argued for Walsh to get life imprisonment, noting he was already in custody "for the term of his natural life".
The judge said Corrective Services NSW officers should not be criticised as they were "deliberately deceived".
Townsend's two daughters were in court on Friday, as their father's bearded killer sat silent - with a visible hearing aid - in his prison greens.
In June 2008, Walsh stabbed his wife and bludgeoned her and his seven-year-old grandson with a hammer.
He drowned his five-year-old granddaughter in a bath at the Cowra home and also drowned the family dog.
When Walsh's daughter came to collect the kids, he attacked her with an axe but she fought him off, suffering serious head injuries.
He will be sentenced for Townsend's murder, his fourth killing, on August 23.
Australian Associated Press