TORONTO — The man who rammed a white rental van into unsuspecting pedestrians on a busy Toronto thoroughfare in 2018, killing 10 people, admits to planning and carrying out the attack.

But Alek Minassian, 28, has pleaded not guilty. His defense: He can’t be found criminally responsible on 10 counts of first-degree murder and 16 counts of attempted murder because he was diagnosed at age 5 with autism spectrum disorder.

That argument, unusual in a Canadian court, is drawing outrage from the autism community. Advocates have denounced it as “egregious”; they warn it could promote unsubstantiated fears about an already vulnerable and misunderstood population.

“We’ll be watching closely because our children and even adults with autism face a stigma,” said Dermot Cleary, the chairman of Autism Canada. “This doesn’t help. … It’s just horribly wrong.”

The judge-only trial, which began last month on Zoom, hinges on Minassian’s state of mind at the time of the attack on April 23, 2018. He killed 10 people and injured scores more, leaving a mile-long trail of carnage in the city’s worst mass killing.

Under Canadian law, defendants can be found not criminally responsible if they prove that it’s more likely than not that they suffered a “mental disorder” at the time of their action that rendered them “incapable of appreciating the nature and quality of the act … or of knowing that it was wrong.”

Such findings are rare here and wouldn’t constitute an acquittal, but could see Minassian sent to a hospital for treatment rather than to prison.

Boris Bytensky, Minassian’s lawyer, has conceded that his client told psychiatrists “some variation of words that amount to the acknowledgment that he understood what he did was wrong.” But he argues that Minassian’s neurodevelopmental disorder meant he could not rationally understand what that meant.

Analysts say they know of only one other time autism spectrum disorder alone was used in a not-criminally-responsible defense in Canada: A youth case in which prosecutors and the defense agreed that it applied.

“This is uncharted territory,” said Jody Berkes, a Toronto-based criminal defense lawyer.

The eight women and two men killed in the attack, who included a great-grandmother who loved the Toronto Blue Jays, a Brazilian steakhouse chef and a Jordanian man who was visiting his family, ranged in age from 22 to 94. One survivor suffered a brain injury that has impaired her ability “to remember the people in her life,” prosecutor John Callaghan told the court. Another had both legs amputated.

Autism spectrum disorder defies simple generalization, analysts say. The number and severity of possible symptoms, which can include fixated interests, repetitive patterns of behavior and challenges in interpersonal relations, vary widely from person to person.

One in 66 children in Canada have been diagnosed with autism spectrum disorder, according to the Public Health Agency of Canada. The U.S. Centers for Disease Control and Prevention estimates that 1 in 54 American children have the disorder.

Sarah Kurchak, an autistic woman, worries that “inaccurate and insidious” ideas about autism spectrum disorder will outlast the trial.

“There is a developing pattern in which (usually relatively privileged) men attempt to blame their violent and criminal actions on an autism diagnosis,” she wrote in Flare magazine, “and the rest of us get painted with the same brush thanks to their craven exploitation of antiquated stereotypes.”

The court has heard testimony from forensic psychiatrists who interviewed Minassian and from his father. Vahe Minassian said his son faced challenges with social interactions, was never violent before the attack and showed no remorse for it. He said that learning that his son had driven the van was like “being struck by lightning on a sunny day — perhaps twice.”

Testimony has also revealed that Alek Minassian has offered sometimes contradictory explanations for his actions to police and psychiatrists.

In an interview shortly after the attack, he told a Toronto police detective that he had been “radicalized” in misogynistic online forums for “incels,” or involuntarily celibate men, and aimed to start an “incel uprising.” A forensic psychiatrist testified that Minassian said he wished there had been “more female victims.”

But other forensic psychiatrists testified that Minassian said he was anxious about starting a new job and was motivated not by a hatred of women but by a desire for notoriety.

Analysts are divided over the viability of his defense.

John Bradford, one of Canada’s most prominent forensic psychiatrists, testified that he did not think Minassian met the not-criminally-responsible threshold because he was not in a state of psychosis or experiencing all-consuming hallucinations or delusions at the time of the attack.

“To get to the type of impact on the operating mind that I’m used to, you need to be psychotic,” he said.

Alexander Westphal, a psychiatrist at Yale, testified this week for the defense. Minassian, he said, displayed a “striking” lack of remorse and empathy, describing the attack “with the dissociative quality of someone playing a video game.”

Westphal said Minassian’s disorder derailed his “developmental trajectory” in the early years of his life, including his ability to understand the moral agency of others and that they could suffer from his actions. He said Minassian was not capable of making a rational choice on the day of the attack.

Minassian “explicitly states the wrongfulness of what he’s doing,” Westphal testified Wednesday. “It doesn’t matter to him because he doesn’t natively see, because he has a defect in social development and empathic understanding of other people, that there are real human consequences … to his actions.”

Westphal read from a report he submitted to the court.

“Despite the fact that he was not psychotic,” he said, “his autistic way of thinking was severely distorted in a way similar to psychosis.”

The defense’s arguments have sparked outrage from advocates for people with autism, who say they’re more likely to be victims of violence than perpetrators of it. Bytensky prefaced his defense by noting this, too.

“There is no psychosis in [autism spectrum disorder] and no tendency to antisocial behavior any more than in the general population,” said Peter Szatmari, the director of the division of child and youth mental health at the University of Toronto’s psychiatry department.

Isabel Smith, a psychology professor in the pediatrics department at Dalhousie University’s medical school, fears Minassian’s defense will do “a real disservice to autistic people.”

“I think it’s dangerous to propose that part of autism would render someone unable to make a moral judgment or to act morally,” she said. “There are differences to how autistic people might reason … that might affect the kind of rationale that they might provide for an action. But to say that’s in any way parallel to psychosis, which implies a disconnect from reality, is potentially dangerous, and it’s certainly unfair.”

Since the trial began, Cleary says, his office has been flooded with heartbreaking messages from concerned parents seeking guidance on how to explain to their children that they won’t become violent criminals because they have autism.

“That’s horrible,” he said.