Before he killed his grandparents, Ross Konidaris was known to walk around late at night with a knife in his pants, talk about people who were out to get him, and search for bombs under his house, a court has heard.
Supreme Court Justice Terry Forrest on Thursday found Konidaris not guilty of murdering his elderly grandparents, Triantafillio and Stavroula Konidaris, on the grounds of mental impairment.
Justice Forrest said he was satisfied Ross Konidaris was not fit to stand trial after evidence from three psychiatrists revealed he was more likely to have been suffering from paranoid schizophrenia, not a drug-induced psychosis, when he gunned down his grandparents in their Yarraville home in the early hours of December 22, 2012.
Because of his mental illness, Konidaris, 25, of Sunshine West, was unaware that shooting his grandparents and setting their house on fire was wrong, the court heard.
When later interviewed by police, his answers revealed a "very disturbed mind", Justice Forrest said.
Konidaris, a regular cannabis user who had taken cocaine and methamphetamines before the shootings, was convinced he had to kill his grandparents after becoming obsessed with a "paranoid fantasy".
He believed his grandfather had once killed a man, that unknown people were out for revenge, and that sharing the Konidaris surname put his own life in danger.
At one point during Thursday's hearing, Konidaris, when sitting in the dock listening to the judge, winked and smiled at his family.
He will remain in the Port Phillip Prison psychiatric unit while a further report on his mental health is prepared. The judge will then have to decide where Konidaris will be held and for how long.
Triantafillio, 81, and Stavroula, 84, had been married for 55 years when they were killed.
Ross Konidaris was armed with a 12-gauge single-barrelled shotgun when he shot Triantafillio twice in the chest.
Stavroula was screaming for her husband when her grandson reloaded and shot her through the heart. He then poured petrol around the house and set it on fire.
Konidaris had had a meal with his grandparents the day before he killed them.
Justice Forrest said family members reported that in the months before the shootings Konidaris had been acting unusually, was not making much sense and expressing paranoid thoughts.
He talked of how people were after him, that he needed to buy a pump-action shotgun and was obsessed with the idea that a bomb had been placed under his younger sister's room.
The judge said Konidaris' father, Jim, talked of how his son would say "weird and silly things" and walk around the kitchen late at night with a knife in his pants.
The court heard Ross Konidaris showed his father what he thought was a bomb under the house, but it was just a piece of coal.
As Ross Konidaris was being led away, Justice Forrest praised the Konidaris family for the way in which they had conducted themselves in court and said he could not imagine what they had been through.
Konidaris continues to have the delusional belief that killing his grandparents was justified, the court heard.