Dr. Julian Gojer told the jury hearing the case it was less likely that Husbands unleashed his 14-shot fusillade as an act of revenge, but rather that the unexpected sight of men who had beaten and stabbed him months earlier was a trigger for his actions, which were likely rooted in fear.
"I don't see revenge as the primary motive here," he said.
Gojer's testimony is significant because it provides insight on Husbands's possible state of mind on the day of the shooting at the Eaton Centre in June 2012.
Husbands's PTSD — which is an important element in his defence — developed after the brutal attack at the hands of men he knew, which took place months before the mall shooting, Gojer said.
"To be assaulted, beaten, stabbed, and to have your face duct taped, not being able to see ... to me that would be an extremely traumatic event," he said, detailing the near fatal February 2012 attack on Husbands. "It's almost akin to torture."
The psychiatrist has interviewed Husbands several times and analysed his prison medical records and psychological tests conducted on him. He has also seen surveillance footage of the mall shooting which has been viewed at the trial.
"Mr. Husbands suffers from post traumatic stress disorder and continues to suffer from post traumatic stress disorder. That's a clinical opinion," Gojer said when asked for his conclusion on Husbands.
Husbands, 25, has pleaded not guilty to two counts of first-degree murder in the shooting and has denied that he went to the mall with the intention of killing anyone.
He has also pleaded not guilty to five counts of aggravated assault, one of criminal negligence causing bodily harm, and one of recklessly discharging a firearm.
The Crown has alleged Husbands gunned down two men at the mall in deliberate retaliation for the stabbing earlier that year.
But Husbands has told his trial that he fired in a blind panic at a group of men he thought were about to attack him. He has also testified that he does not remember exactly what happened in those moments.
He has said he recalls hearing a loud bang and that everything "got kind of dark." He has also said he doesn't remember bolting from the food court in the moments after the shooting.
Gojer — who was called to testify by the defence — said Husbands's testimony is typical of someone with post traumatic stress disorder experiencing a flashback, which he called a "diassociative episode."
Confirming that Husbands had reported having flashbacks between being stabbed and the incident at the mall, Gojer added that it would not be uncommon for him to have another flashback at the time of the shooting.
"You've got to ask yourself the question, is there a new traumatic event that has the capacity to trigger disassociation?" Gojer told the jury, suggesting that the sight of his former attackers could have pushed Husbands into a "fight or flight mode."
Gojer also said someone with PTSD would view their environment in a different light.
"It's almost like you have a new set of lenses that you are wearing where the world is no longer a safe place. The world is now a dark and moody place," he said. "There's also a sense of helplessness...it's a terrifying feeling."
An individual with PTSD might also develop a sense of paranoia, Gojer added.
"If you become paranoid with respect to a group of individuals who stabbed you or attacked you and these individuals are still at large in the community, the paranoia that you have is a more realistic paranoia," he said.
Husbands's lawyer said outside court that he will be bringing evidence before the trial of a lack of criminal responsibility on his client's part.