CALGARY - The Crown agrees a young man was suffering from a mental disorder when he stabbed five people to death at a Calgary house party two years ago.

The two psychiatrists and psychologist who testified last week at Matthew de Grood's trial did careful, thorough work and have vast experience dealing with such cases, prosecutor Neil Wiberg said during his closing arguments on Tuesday.

"As an officer of the court, I do not take issue with the reports that are provided by these three experts," Wiberg told the packed courtroom.

"I agree that the accused was suffering psychosis, which qualifies as a disease of the mind, on a balance of probabilities. And I also agree that on a balance of probabilities, the accused was incapable of realizing his acts were morally wrong."

The trial heard evidence that de Grood became withdrawn about a month before the attack on April 15, 2014 and started posting about the end of the world, religion, vampires and Darth Vader on Facebook.

He reported hearing voices telling him to kill and believed the end of the world was coming before he grabbed a knife from a kitchen in the northwest Calgary home and stabbed the victims to death.

Killed in the attack were Kaitlin Perras, 23; Lawrence Hong, 27; Josh Hunter, 23; Zackariah Rathwell, 21; and Jordan Segura, 22.

Defence lawyer Allan Fay said in his closing argument that his client believed he was defending himself from werewolves and vampires at the time.

"Some might question the manner in which he did it. The stabbings seem somewhat purposeful, but Mr. de Grood explained that in his delusions, he believed that the only real way to kill demons of this nature was to stab them in the heart," Fay told the court.

"He was not trying to be cruel. He was trying to do this as best he could under the circumstances. He truly believed that his life would be forfeit if he did not."

Wiberg said the experts weighed all possible alternatives — including that de Grood may have been feigning mental illness or intoxicated — before coming to the conclusion that de Grood, now 24, was suffering psychosis at the time of the killings.

"There was a rapid descent into that state where he committed these five murders," said Wiberg. "They were done with brutality and ruthless efficiency. The psychotic episode that affected his mind did not reduce his effectiveness as a killing machine."

Alberta Justice Eric Macklin is to release his verdict on Wednesday.

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Note to readers: This is a corrected story. A previous version attributed the quote to Neil Wiberg

News from © The Canadian Press, 2016