Eric James Forrest was found guilty of murdering David Collisson, 53, on a rural property near Mudgee, in central western NSW, in September 2023.
Now 35, he had photographed himself with a double-barrelled shotgun hours before he turned the loaded weapon on Mr Collisson while they were standing on a secluded hill.
"You want to treat me like a f***ing gronk?" he asked.
The older man pleaded for his life, telling Forrest they were brothers and he loved him.
But the gunman disregarded the pleas and shot Mr Collisson in the chest or shoulder, causing him to fall backwards onto the ground.
A witness described the injured man rolling around emitting a horrendous squealing noise before Forrest went back to his car and reloaded the shotgun with two further rounds.
He chased after Mr Collisson, who was attempting to escape after regaining his feet, and shot him twice more.
The dead man's body was later moved into a large hollow tree stump which Forrest set on fire.
The gruesome details of Mr Collisson's last moments were laid bare in the NSW Supreme Court as Justice Dina Yehia sentenced his murderer to 30 years behind bars.
The precise motive for the unprovoked murder remains a mystery, she noted.
Forrest had been angry with the older man for an unknown reason and decided to kill him shortly before firing the first shot, the judge determined.
"Once that shot was discharged, the offender persisted in pursuing the deceased and discharged the firearm again in what was a brutal and cold-blooded act," she said.
The killing shook the lives of Mr Collisson's family, who described their grief and devastation over his death.
His son described the profound loss he feels at losing his father in such a violent act, telling a psychologist it made him question his own safety and trust in others.
Mr Collisson's family were unable to bury his body because his bones had been destroyed beyond recognition in the fire, the court was told.
Justice Yehia acknowledged the family's loss and said no sentence could adequately capture the value of his life.
"No gaol term, of any length, can return a loved one," she said.
She sentenced Forrest to a minimum of 20 years behind bars.
He will be the same age as his victim when he is eligible to apply for parole.
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