Alexandre Bissonnette cut a low profile as a shy, withdrawn political science student, keen on far-right ideas.
Now, he stands accused of gunning down six worshippers at a Quebec mosque in one of the worst attacks ever to target Muslims in a western country.
The 27-year old grew up in a quiet suburb of Quebec City, posting online about friends, family and food.
He studied anthropology and political science at nearby Laval University, and most recently lived in a fourth-floor apartment with his twin brother that neighbors described as often noisy.
The apartment is one kilometer (0.6 miles) from the Sainte-Foy mosque where Bissonnette allegedly shot worshippers in the back.
His Facebook account has since been deleted, but an analysis of stored pages by SITE Intelligence Group -- a US-based organization that monitors extremists' activities -- described his posts as "largely apolitical."
"It is a cruelly banal profile that resembles many others and it is extremely difficult to perceive the evolution," David Morin, co-director of the Observatory on Radicalization and Violent Extremism, told AFP.
Bissonnette went to classes at Laval University, read the essays of French poet Charles Baudelaire, and worked part-time at the province's blood collection agency. It has expressed alarm over learning that one of its employees was suspected in the mosque shooting.
Although Bissonnette was not affiliated with any group, he appears to have embraced a "right-wing, a bit reactionary, somewhat anti-immigrant, anti-feminist ideology," said Morin.
He espoused positions taken by US President Donald Trump, French National Front leader Marine Le Pen, and a Quebec group that rejects multiculturalism.
SITE Intelligence Group noted that on his Facebook page, "There were no posts about Al-Qaeda, the Islamic State (ISIS), or Muslims, nor were there any posts related to immigration."
But he "liked" the pages of Le Pen, Trump and Quebec's Generation Nationale.
Morin said it is always hard to determine exactly what will lead to a person's break with reality, to an existential crisis, insecurity about their identity, and a need for self-affirmation.
In fact, this young man "may not even have been radicalized" to nationalist ideas. In a moment it is likely simply "the light went out," he said.
This might explain why after allegedly carrying out these murderous acts, Bissonnette fled and called police to turn himself in.
Morin suggests parallels with a case in the US state of South Carolina in which Dylan Roof shot dead nine black parishioners at a church in 2015.
Profiles of the suspects in both cases run contrary to the fanatics who typically commit suicide, including blowing themselves up during or after an attack.
There were no obvious signs of Bissonnette's predilection for violence. Prior to Le Pen's controversial March 2016 visit to Quebec City, he showed little interest in politics, despite majoring in it at school, his friends told local media.
Former classmates described him as a quiet, unassuming guy who blended in. Others said he was introverted, socially awkward and frequently bullied in high school, but that he brushed it off.
People who knew him described him as having lately become a xenophobe, an ethnic nationalist and an online troll, but not a racist.
He denounced, for example, the flood of Syrian migrants into Europe last year.
"He was someone who made frequent extreme comments in social media denigrating refugees and feminism. It wasn't outright hate, rather part of this new nationalist conservative identity movement that is more intolerant than hateful," Francois Deschamps, who runs a refugee-support Facebook page, told the daily Globe and Mail.
One of Bissonnette's last online postings was a photo circa 2002 of himself as a boy in a military cadet uniform, stone-faced.