Joshua Bainbridge was cutting down trees with his father Colin at a regional Victorian property when he heard yelling.
He rushed over to his 66-year-old father and found disgruntled neighbour Stuart Lee covering him in petrol and setting him alight.
"Seeing my father ignite and scream as he was burned alive is a memory that will never leave my mind," Joshua Bainbridge told the Victorian Supreme Court on Wednesday.
Lee, 65, has pleaded guilty to murdering Colin Bainbridge at the Wheatsheaf property near Daylesford on March 14, 2023.
Mr Bainbridge had been felling trees in his friend's backyard when, without any instigation, Lee yelled at him to "f*** off".
Mr Bainbridge said the same thing in response and Lee rushed off to call the police but five calls to the Daylesford station went unanswered.
His final call was diverted to Bacchus Marsh police who told him to call triple zero if he needed immediate assistance.
Lee told the officer he would go and murder his neighbours if they did not come.
The 65-year-old then went into his shed, poured petrol from a jerry can into a blue bucket and grabbed a lighter from inside the house.
Lee went into the backyard, climbed a fence and poured the petrol over Mr Bainbridge before setting him on fire.
Joshua Bainbridge rushed over and tried to put out the flames with his jumper but was unsuccessful so he retrieved a hose.
His father said "I can't believe this bastard has done me in" as Joshua called triple zero for an ambulance.
Lee also called emergency services but for police attendance, saying he poured petrol on his neighbour because he was trying to defend himself.
Mr Bainbridge was airlifted to The Alfred with burns to 81 per cent of his body and he died in hospital later that evening.
Joshua Bainbridge told the court he was perpetually stuck reliving his father's final day.
"I feel like I'm balancing on a knife edge," he said.
His father was a good man who changed many people's lives for the better, Mr Bainbridge said.
"He was robbed of the last years of his life for nothing," he said.
"The world is a worse place without him in it."
Psychiatrist Andrew Carroll told the court Lee had a personality disorder where he was paranoid, suspicious of others and felt like he was under threat.
Dr Carroll said there was a realistic link between Lee's disorder and his offending, and the 66-year-old had a lack of empathy and shame.
"He has no real sense of guilt because he feels he was justified to do what he had to do," the psychiatrist said.
Lee was not psychotic at the time of the crime and his presentation did not meet a diagnosis of psychopathy, Dr Carroll said.
Lee's lawyer Julia Munster conceded the murder was horrific and warranted a significant jail term.
She will make further submissions on Thursday but Justice Andrew Tinney already flagged he was considering life in prison as a possible sentence.
