TORONTO --  In a virtual trial completed remotely, a 33-year-old Toronto man has been found not criminally responsible for killing his grandmother and trying to kill a health-care worker.

Justice John McMahon, from his home, found Michael Colatosti suffered from a "major mental illness" and did not know right from wrong when he killed Elena Marcucci, 84, and repeatedly stabbed Osayuki Erhabor on Aug. 18, 2018.

"This tragic killing and attempted killing are completely without motive," McMahon said.

Colatosti believed his grandparents were robots sent to destroy both him and the earth, according to an agreed statement of facts read out by Crown attorney Patrick Travers.

At 6:30 p.m., he stormed out of the basement of his grandparents' house, where he lived, armed with a kitchen knife.

"You are going to die today!" Colatosti screamed as Marcucci and Erhabor tried to safeguard themselves in a bathroom, court heard.

Colatosti repeatedly stabbed his grandmother and then Erhabor, who fell to the ground but was able to escape when Colatosti went into another room.

His grandfather, John Marcucci -- blind, in a wheelchair and suffering from dementia -- did not move but heard the attack, court heard.

Marcucci died five weeks after his wife was killed, "no doubt of a broken heart," the judge said.

Court heard Colatosti had no criminal record and began to show signs of mental illness two years before the killing when he put his father in a headlock. Colatosti stopped communicating with his parents and moved into his grandparent's home in Toronto's west end.

Colatosti helped his ailing grandfather and cared for him at night while a personal support worker helped during the day, court heard.

There was no animosity between Colatosti and his grandmother, nor between him and Erhabor, and no financial gain to be made, the judge said.

Colatosti appeared by video from the Toronto South Detention Centre to the judge, the Crown and his lawyer. Media and the families of the victims listened in on a conference call.

"I ask for everyone's patience as we try to figure this out," McMahon told the conference call as the court struggled early in the proceedings with audio feedback and difficulties connecting with the jail.

After 40 minutes, the trial got underway.

The defence had requested to proceed on the initial first-degree murder charge without a jury. The Crown agreed and received permission from the Attorney General.

Otherwise, the proceedings would not have occurred because jury trials are temporarily banned due to the COVID-19 pandemic.

Travers, the Crown attorney, told court there was no evidence of planning and deliberation, so the case proceeded on a second-degree murder charge and attempted murder, to which Colatosti pleaded not guilty.

Both the Crown and defence said Colatosti should be found not criminally responsible for his actions.

"We have evidence that Mr. Colatosti was under the delusion the end of the world was happening and his grandparents were really just impostors that turned into robots that were malevolent, and he had to act out," Travers said.

Court heard Dr. Ian Swayze, a forensic psychiatrist, examined Colatosti and concluded he suffered from a major mental disorder before, during and at least a month after the killing.

Swayze diagnosed Colatosti with what's known as an unspecified psychotic disorder and a severe substance use disorder.

Court heard Colatosti used to smoke four grams of marijuana a day -- the equivalent of 13 joints or "24 significant bong hits," said his lawyer, Robert Karrass.

The marijuana use affected Colatosti's mental health, according to the psychiatric report, though it did not cause his condition.

"But for the marijuana use, it is unclear if his condition would have spiked to this moment," Karrass said. "But it's not the marijuana use that caused the condition, but the underlying psychotic condition."

The prosecution read out victim impact statements filed by Erhabor and members of Marcucci's family.

"I no longer find happiness that I used to enjoy," Erhabor wrote. "In short form, life has not been favourable to me. Sometimes I wish I was never born."

She said her left arm no longer functions well due to permanent nerve damage and she cannot afford her medication. She said she is in serious pain and has "scars all over me" from the stabbing.

Marcucci's relatives said Elena had been the matriarch of the family.

"Our hearts are broken. Our wonderful Elena held us together like glue," the Marcucci and Colatosti families wrote.

Colatosti will eventually be moved to a secure wing at a Toronto mental health hospital, but the institution is not accepting anyone right now due to the pandemic, court heard, so he will remain in jail in the interim.

This report by The Canadian Press was first published April 15, 2020.