Open this photo in gallery Alek Minassian.

The passage of a full day added new layers to the profile of the man accused of perpetrating the worst mass murder in decades in Canada – a young man with developmental disorders who failed as a military recruit and publicly embraced a toxic misogynist ideology.

Alek Minassian, 25, appeared in a north Toronto court Tuesday morning wearing a white police-issued jumpsuit to face 10 counts of first-degree murder and 13 counts of attempted murder. He was arrested Monday afternoon minutes after a white van drove more than two kilometres down Yonge Street in the northern part of Toronto, hitting pedestrians along the way.

Part of Mr. Minassian’s mental state was visible during his arrest. Video captured at the scene showed him pretending to reach for and point a gun at a police officer while challenging the officer to shoot him in the head. But evidence the expert in computers was troubled had previously emerged among friends, colleagues, teachers and other acquaintances and in public. The common theme is rejection.

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Within minutes of learning of the attack and the suspect’s identity, Facebook took down Mr. Minassian’s account. The alleged attacker had posted praise for a mass murderer in the United States who was part of the “incel” movement – a women-hating collection of “involuntarily celibate” men in online forums and other sites frustrated by their lack of success sexually attracting women.

“This is a terrible tragedy and our hearts go out to the people who have been affected,” Meg Sinclair of Facebook Canada said by e-mail. “There is absolutely no place on our platform for people who commit such horrendous acts. We have found and immediately deleted the suspect’s Facebook account.”

Toronto Police Homicide Detective Sergeant Graham Gibson said the “cryptic Facebook post” belonged to the suspect, but added that the police are not currently investigating any particular group or movement.

Mr. Minassian’s post was fashioned as a military-style report for duty praising Elliot Rodger, who killed three men and three women in the United States in 2014 saying he wanted to punish women for rejecting him.

Different videos posted to Twitter show a man being arrested in possible relation to an incident where a van mowed down pedestrians in Toronto's north.

Quebec mosque shooter Alexandre Bissonnette also took interest in Mr. Rodger. Less than 24 hours before the mosque shooting in January, 2017, he typed “Elliot Rodger” into Google, according to evidence produced during his sentencing hearing. A psychologist testified the mosque killer identified with the U.S. murderer.

Mr. Minassian’s Facebook message contained codes and a message echoing formats used by the Canadian Armed Forces. The Canadian military confirmed Tuesday that Mr. Minassian enlisted on Aug. 23, 2017, and attended basic training in Saint-Jean-sur-Richelieu, Que., as all new CAF recruits do. He requested to be voluntarily released after 16 days of basic training, the CAF said.

A New Brunswick resident and former recruit who was a bunkmate with Mr. Minassian said the suspect went to the hospital to be treated for a virus during his brief military time. He said Mr. Minassian did not associate with other recruits and was very quiet.

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Mr. Minassian never received weapons training, he said, but was about a week from being issued a rifle and would have had live-fire training a short time afterward. The fellow recruit, who washed out of basic training due to illness, did not want to be identified because he plans to enlist again.

Harjit Sajjan is defending the military’s selection process after it was revealed that the Toronto van attack suspect was briefly a Forces member. The defence minister said Alek Minassian served for two months. The Canadian Press

Mr. Minassian attended Seneca College where he was known as an expert in computer chips before completing his course in the past month. He focused on graphics processing units, which have re-emerged in prominence in recent years as a cornerstone of artificial-intelligence technology.

Classmates described a seven-year journey to complete his course that included many wild academic swings – he left the program for at least a year at one point, but also had high marks at times – along with emotional ups and downs.

Friends, classmates and a former teacher said he had a form of autism along with social anxiety and mental-health issues.

His own mother described her son as having Asperger syndrome – but that terminology is no longer used in medicine. Rather, people who were said to have Asperger are now diagnosed with autism-spectrum disorder and deemed high-functioning.

“He was afraid of girls and very shy in general,” said Nikki Feinstein, a former high school classmate who is now a teacher. “He didn’t say much, but when he did he was difficult to understand because of his cognitive disabilities.”

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Robin Holloway, a psychologist who specializes in treating youth with autism-spectrum disorder, said having autism or other social or mental disorders is not a cause of violence. But, he said, there are rare cases he has labelled “uninhibited/aggressive” types who “over the years have built up a list of grievances based on being scorned, rejected, bullied, including sexually” and are prepared to act.

“They have built up a tremendous volume of internal anger … and want others to experience their suffering and mental agony in the way they experienced it,” said Dr. Holloway, author of Asperger’s Children: Psychodynamics, Aetiology, Diagnosis and Treatment and a clinician at Toronto’s Willow Centre. “Vengeful fantasies can turn into horrible reality.”

Dr. Holloway stressed he has only seen a handful of violent uninhibited-aggressive cases of mild autism in his 30 years of practice, and that they can be treated with proper intervention, time and sufficient resources.

Along the leafy, upper-middle-class street where Mr. Minassian shares a home with his parents, meanwhile, residents say the family is well regarded and often helps out shovelling snow from neighbouring properties.

Next-door neighbour Ramak Askara said he always assumed Mr. Minassian suffered from some sort of mental illness. “He was quiet, always home, always with his dad,” Mr. Askara said.

As of Tuesday morning, yellow police tape still surrounded the Minassians’ brick home, and three squad cars from the Toronto Police Service and York Regional Police were stationed outside.

With reports from Justin Ling, Ann Hui, Molly Hayes, Jeff Gray and Ingrid Peritz