When he saw a man holding a knife to a woman's throat, 72-year-old Keith Harold Allen made a judgment call and shot him.
It was almost certainly the right thing to do, a NSW Supreme Court judge says.
The actions of Allen, who spent two and a half years in custody and is now terminally ill with lung cancer, were vindicated in court on Wednesday, when Justice Michael Adams handed down his reasons for acquitting the elderly man of murder last week.
Allen shot 35-year-old Todd Sutton in the head after Mr Sutton threatened to kill Allen's landlady and boss on a farm near Mudgee in NSW's central west on December 4, 2010.
The seven-day trial heard Mr Sutton chased the woman, who was his partner, around the yard with a blockbuster - a type of axe - before cornering her in the kitchen and leading her outside, holding a knife to her throat.
Allen, who worked as a greyhound keeper on the property, fired two shots in quick succession, hitting Mr Sutton first in the shoulder and then in the head.
He then told the woman to call police, walked back to his caravan, sat down and had a beer before making his own triple zero call.
"There's no problem with me darling," Allen said in the phone call played during the judge-alone trial.
"I'm sitting here calmly."
He told police he was distraught that he had taken a man's life, but that he opened fire to stop Mr Sutton cutting the woman's throat.
The crown case was that while Allen's first shot was fired in defence of the woman, the second was done with intent to kill, after Mr Sutton had let her go and was no longer posing a threat.
But Justice Adams did not accept Mr Sutton had let go of the woman after the first shot and said the evidence of a child who was on the property at the time was not reliable on that point.
He said Mr Sutton was "drunk and enraged" and Allen "made a judgment call ... that was so far from being wrong, let alone criminal, that it was almost certainly right".
"He acted from beginning to end to protect (her) from sustaining very serious injury and possible death and he did so reasonably, considering the means he had at his disposal," Justice Adams said.
Allen was convicted of three firearm offences but released from custody last week.
He was not in court for the judgment on Wednesday.