A jury of 12 has found Canadian soldier Howard Richmond guilty of first-degree murder for stabbing his wife to death in July 2013.

The jury in the Ottawa trial began deliberating on Nov. 18 after hearing conflicting evidence about Richmond's mental health over the course of a trial that lasted more than seven weeks.

After nine days, the jury returned Thursday afternoon with its guilty verdict, which carries a mandatory life sentence.

Richmond showed no reaction to the verdict. His sister and nephew, who were in the courtroom, were visibly upset as the verdict was delivered.

Richmond, 53, admitted to stabbing to death 28-year-old Melissa Richmond in a ravine near Ottawa's South Keys Shopping Centre in July 2013, but pleaded not guilty to first-degree murder at the outset of his trial in September.

Defence lawyer Joe Addelman argued that Richmond became "a broken man with a broken mind" following six tours of duty that left him with post-traumatic stress disorder.

But Crown prosecutor Suzanne Schriek argued that it was a case of a jealous husband who consciously killed his wife after discovering she was having an affair.

Ontario Superior Court Judge Douglas Rutherford had instructed the jury of four men and eight women that if they believed Richmond's mental disorder "robbed him" of understanding the nature and quality of his actions it meant he is not criminally responsible and their deliberations end there.

But he said if the jury determined he was criminally responsible, they could find him guilty of either first- or second-degree murder. The jury could also find him guilty of manslaughter if they determined he did not intend to kill his wife.

'She never hurt a soul'

After the jury delivered its verdict, Ottawa Police Service Det. Chris Benson, the lead investigator in the case, read a victim impact statement on behalf of the family.

"You think jail is hell, try living the past 28 months trying to wrap our heads around having to bury our 28-year-old daughter. She never hurt a soul, never did anything bad to anyone," said part of the statement that Benson read.

"Every time your cell door slams shut, may it be a reminder to you of what you did — taking her life. There was absolutely no justification for murdering Melissa."

The statement also spoke of her smile and "giddy laugh," and how her parents had stopped celebrating all birthdays and holidays in the wake of their daughter's death.

"You don't deserve the privilege of being a free man ever again," the statement concluded.

A copy of the victim impact statement read Thursday after Howard Richmond was convicted of first-degree murder in the death of his wife Melissa. (CBC)

Following the victim impact statement, Rutherford asked Richmond if he had anything to say.

Richmond's lawyer conferred briefly with him and simply answered, "No."

After that statement, Rutherford told Melissa Richmond's family that they had "the sympathy of the court and all present here."

Outside the court, Benson shared his thoughts on the verdict.

"It's quite obvious this wasn't a case of PTSD or mental health. This was a straight case of domestic violence, and a young woman's life was taken away out of mere jealousy," said Benson.

Mental health experts clash

Mental health experts for the defence and the Crown clashed over the soldier's diagnosis during the course of the trial.

Forensic psychologist Charles Ewing testified it took Richmond nine months to realize in a gradual unravelling of memories that he killed his wife, because he was suffering from traumatic amnesia.

Richmond testified he hid in the bushes with a knife and screwdriver that were meant to help him cut off his wife's clothes during a consensual role-playing sex game they planned together as a couple. He said a loud noise triggered a flashback of his military tour in Croatia, where he witnessed an 11-year-old girl being executed.

Ewing testified that Richmond experienced a dissociative flashback before the killing, but psychiatrist Derek Pallandi challenged the notion that a loud sound could prompt "homicidal behaviour."

Pallandi suggested that the smell of Melissa's blood could have prompted a flashback after the killing, but said that Howard was not "psychologically absent" because he recalled details of the actual killing.

Husband denies knowledge of affair

Melissa Richmond's lover, Jeff Thornton, testified that she had worried her husband would kill her if he found out about the affair.

Thornton said that "she wasn't joking" when she told him her body would never be found if her husband learned she was cheating. He also said she planned to leave her husband days before she was killed.

Howard Richmond testified during the trial that he didn't find out about the affair until after he killed his wife.

When confronted with the affair during a police interview in the days following her death, Richmond repeatedly denied that he killed her.

"No act justifies that kind of violence," he told police.

Soldier researched PTSD

An Ontario Provincial Police computer forensic analyst testified that Richmond researched PTSD in seven separate online queries hours after he killed his wife, including one search about flashback recovery.

Court also heard that Richmond posted about "voices" in his head on Facebook after the killing.

Richmond reported his wife missing on July 25, 2013, saying she went for a late-night drive on July 24 and never returned to their home in Winchester, Ont., located about 40 kilometres south of the shopping centre where her body was eventually found on July 28.

Police found a knife and a screwdriver wrapped in bloody clothes in the basement of the Richmonds' home. The bundle was wedged between the ceiling rafters and the furnace duct in the basement.

The Crown argued he was conscious of his guilt when he hid the weapons, while the defence argued his mental disorder left him unable to appreciate what he was doing.