Instead, the 59-year-old grabbed a shotgun and drove off with his sons George, 22, and John, 18, to a southeast Melbourne home where DJ equipment they had rented out through their business was being advertised for sale on Gumtree for $3500.
Panagiotou on Friday faced Victoria's Supreme Court, where he was jailed for a total of nine years after pleading guilty to the manslaughter of Duane Hutchings, 46, whom he shot once in the head from close range at the Oakleigh East residence in February 2019.
Justice Lex Lasry described the killing as an act of "tragic stupidity".
"When you were woken up by your sons and informed of their intention ... instead of dissuading them from their plan you joined them and brought a firearm," Justice Lasry said.
"You then voluntarily entered a confrontation with a loaded and cocked shotgun, understood the dangerousness of brandishing that weapon and must have understood that your actions would be terrifying for the occupants.
"Your actions made the catastrophe which occurred inevitable."
Mr Hutchings, a father-of-six, was not involved in the Gumtree scheme but instead had been visiting the woman allegedly behind it.
Panagiotou and several others began assaulting him after confirming the DJ equipment was inside her home.
The 59-year-old later told police he raised his gun when he thought he saw Mr Hutchings reach for a weapon.
He also claimed that he didn't mean to pull the trigger.
The group fled after packing up the DJ equipment and telling Mr Hutchings' friend to wait five minutes before calling an ambulance.
"I took a man's life, I'm not a good person. Look what I've done," Panagiotou told police.
His lawyer Malcolm Thomas said Panagiotou had experienced absolute shame and self loathing since the killing.
He said he experienced hyper-vigilance and obtained the weapon after a home invasion in 2006 which had a lasting impact on his mental health. He just wanted to protect his children.
Police had already told them not to go, after attempts were made to report the equipment stolen. Officers told them they couldn't follow it up because it was a civil matter.
"This was most unfortunate in view of what followed," Justice Lasry said on Friday.
Panagiotou, a former nightclub owner, was originally charged with murder and had been set to stand trial before he pleaded guilty to manslaughter in October.
He must serve at least six years behind bars before being eligible for parole but has already spent nearly three years in custody.
