Kilby, 40, has pleaded guilty to murdering Andrew John Anthoney in Peak Hill, central western NSW, on March 11, 2023, nine days after stealing a mobile phone from the victim's house during a drinking session.
In the days between the theft and the murder, Kilby told friends he found child abuse material on the phone and accused Mr Anthoney of being a pedophile, according to a statement of facts before the NSW Supreme Court.
After being arrested and freed on bail for an unrelated crime on March 11, Kilby went to the Peak Hill RSL, where he was seen drinking, smoking, dancing and singing to himself.
He then walked to Mr Anthoney's house to confront him about the images he claimed were on the stolen phone and the pair had an argument.
Kilby punched and stomped on Mr Anthoney several times, leaving him bleeding and unconscious near the kitchen.
"I think I've killed someone," Kilby was heard saying as he ran away from the house.
Kilby's cousins told police the long-time drug user had been "off his head" on ice and was acting strange in the days before the murder.
Public defender Nicholas Broadbent SC on Monday told the Supreme Court the killing was not an act of vigilantism, as suggested by prosecutors.
"The court could not be satisfied Mr Kilby entered the house with the intention of taking the law into his own hands," Mr Broadbent told the court, sitting in Orange.
"There was an argument which then escalated. Mr Kilby states that he just lost it."
Kilby grew up in a violent home and was exposed to drugs from a young age, going on to develop a "conduct disorder" that led to anti-social behaviour, according to a psychologist's report.
While on remand at the Macquarie Correctional Centre in Wellington, Kilby had made personal progress, obtaining engineering qualifications, participating in cultural groups and becoming the jail's Aboriginal delegate.
In a handwritten letter to the court, Kilby acknowledged the pain he caused Mr Anthoney's family and his own.
"I hope one day I can show that I can be a better man," he wrote.
Mr Anthoney's sister Katrina read a brief victim impact statement, saying the killing in "dire" circumstances had shattered their family.
"It's a real life tragedy for all involved and such a shocking and senseless death," Ms Anthoney said.
"His family are the quiet voices who are saying: our loss is not OK in a civil society."
Justice Dina Yehia will sentence Kilby on July 14.
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