Lawyers for Alexandre Bissonnette, who killed six people in a Quebec City mosque three years ago, tried to convince the province's highest court on Monday to lighten his sentence by arguing he was not driven by a hatred of Muslims.

Bissonnette's legal team, led by Charles Olivier Gosselin, offered the Quebec Court of Appeal a portrait of a mentally troubled young man who needed a target for his violent rage.

When Bissonnette was sentenced in 2019, after pleading guilty to six counts of first-degree murder and six counts of attempted murder, the judge in the case identified his motive as a "visceral hatred toward Muslim immigrants."

That formed part of the judge's justification for handing Bissonnette a life sentence with no chance of parole for 40 years, the longest sentence in Quebec history. Bissonnette will be 67 when he's eligible for parole.

But Gosselin said the judge's characterization ignored much of the evidence that was presented during the sentencing hearings.

Bissonnette had been suicidal since his teens. He had fantasized for years about committing a mass shooting and, two months before attacking the mosque, entered a Quebec City mall carrying two pistols with the intention of shooting others and himself.

Gosselin acknowledged his client accessed far-right and Islamophobic material online before the attack, but said Bissonnette was seeking a "rationalization" for his obsession with killing.

Gosselin accused the original judge, Superior Court Justice Francois Huot, of taking a "pick-and-choose" approach to the facts about Bissonnette's personality, and of making a mistake by describing his client as a racist.

"That wasn't the motivation for his crime. There is no proof of that," Gosselin told the judges. "It's as if he was describing someone else."

The office of Quebec's chief prosecutor is also appealing Bissonnette's sentence, and also presented its arguments Monday in Quebec City.

Crown prosecutor Thomas Jacques, who represented the Crown at the original sentencing hearing, argued Bissonnette's crimes are so heinous that an additional 10 years should be added to his sentence.

"It was possibly the worst hate crime in Canadian history," Jacques said.

In his presentation to the court, Jacques countered the claim that Bissonnette's mental health made him deserving of a more lenient sentence.

Six men died in the attack. They are, clockwise from left, Mamadou Tanou Barry, Azzedine Soufiane, Abdelkrim Hassane, Ibrahima Barry, Aboubaker Thabti and Khaled Belkacemi. (CBC)

Contrary to the portrait provided by Bissonnette's lawyer, Jacques described him as someone who gradually developed a plan to commit hate-based mass murder.

Bissonnette began buying weapons and ammunition in 2015. The following year, he decided he should kill "terrorists." Around three months before the shooting, Jacques said, Bissonnette identified Muslims as his target.

After that followed a flurry of online research about the suburban Quebec City mosque that he eventually attacked, the Quebec Islamic Cultural Centre.

"His mental health issues don't obliterate the hateful character of his actions," Jacques said. "He chose his victims based on his prejudices about Muslims."

Also arguing for the Crown was Pierre Bienvenue, who said: "The only reason he didn't kill more people is that his gun jammed and he ran out of bullets."

Bissonnette was not in the courtroom on Monday. His parents, though, were present, often leaning forward in their seats to hear what was being said about their son.

Family members of the victims sat on the other side of the mostly empty room.

Under his current sentence, Bissonnette will be eligible for parole when he turns 67. (Hélène Bernier)

Lack of guidelines

In pushing for a longer sentence, the Crown has to defend a controversial measure in the Criminal Code — introduced in 2011 — that gives judges the power to hand down consecutive sentences.

Under that measure, Bissonnette could have been sentenced to 150 years without parole; 25 years for each count of first-degree murder.

But Huot, the sentencing judge, questioned the constitutionality of such a long sentence, and opted for 40 years instead — five concurrent life sentences and one additional 15-year sentence.

Though other mass killers in Canada have been sentenced under the provision, no appeals court has yet had to rule on its legality.

"We are looking for guidelines for the whole legal community," Jacques told the judges.

Bissonnette's lawyers want consecutive sentences to be struck from the Criminal Code altogether. They say that at 40 years — 15 years longer than the usual life sentence — Bissonnette's sentence violates his charter right against cruel and unusual punishment.

"Democracies similar to ours are moving away from such sentences," Gosselin said. "The sentence goes too far. It goes against the Canadian values recognized by the charter."

It will likely be several months before Quebec's court of appeal hands down a decision about Bissonnette's sentence.

On Wednesday, Quebec City's Muslim community will gather to mark the third anniversary of the mosque attack.