In recent years he had been working as a miner and labourer in British Columbia. Home was at times a Salvation Army shelter and he was estranged from his parents, and alarmed fellow worshippers at the local mosque with both his talk of demons and his plans to travel to the Middle East.
"We were having a conversation in a kitchen and I don't know how he worded it: He said the devil is after him," Dave Bathurst, a friend and fellow convert, recalled in an interview with the Globe and Mail. "I think he must have been mentally ill."
Bathurst last saw Zehaf-Bibeau praying six weeks ago at the mosque from which elders had asked him to stay away because of his "erratic" behaviour.
In one incident, he was arrested near the Masjid Al Salaam religious centre in Burnaby after making violent threats to a business owner.
He is believed to have called the police and demanded to be arrested on an outstanding warrant in Quebec that did not exist because he wanted to be housed in police cells.
Upon being told that police could not respond to a crime that had not been committed, Zehaf-Bibeau made threats to an unknown person in a bid to be picked up by police.
He was remanded for a bail hearing and kept in custody for 66 days, during which time he underwent at least one psychiatric test that deemed him fit enough to enter a guilty plea for uttering threats, according to court documents.
For Zehaf-Bibeau, who had been sleeping at times in the mosque, it was a far cry from his youth in the affluent Montreal neighbourhood of Laval.
Court records show that he had a long previous history, with a string of convictions for assault, robbery, drug and weapons offences, and other crimes.
In Montreal, his parents' house has been empty since the news of his rampage broke. But breaking her silence, his distraught mother Susan Bibeau expressed her remorse and horror for her son's actions while saying that she could throw no light on his motives.
She said that she met him last week for the first time in five years.
"So I have very little insight to offer," she said.
On behalf of her and her husband, Bulgasem Zehaf, she said that she was crying for those her son had hurt so terribly, not for his death.
"No words can express the sadness we are feeling at this time. We send our deepest condolences to [the victim's family] although words seem pretty useless. We are both crying for them.
"We also wish to apologise for all the pain, fright and chaos he created. We have no explanation to offer."
She said that she was "mad at our son" and "part of me wants to hate him at this time". But she also said that he seemed lost "and did not fit in".
Bibeau's mother has spent her life working to help refugees and immigrants integrate into Canada, a country that long prided itself on its open multicultural society.
She has spent nearly 25 years working at the Immigration and Refugee Board of Canada, rising to the rank of department director-general.
She did not explain why she had not seen her son for so long, although he is believed to have been living in western Canada for at least three years.
He also spent time in Libya in 2011 during the uprising that overthrew Colonel Muammar Gaddafi, quite possibly at the same time as his father.
In 2011, a Washington Times reporter in Libya interviewed a man from Montreal called "Belgasem Zahef" who had travelled from Canada to join the rebels fighting the long-time dictator.
Zehaf-Bibeau told Bathurst that he has wanted to go to the Middle East when the two men saw each other for the last time at the Burnaby mosque six weeks ago.
He insisted that his motive was simply his desire to study Islam and learn Arabic, familiar claims made by extremists to provide cover for their travels.
Bathurst was apparently not convinced, urging his friend to make sure that his focus was indeed study "not something else".
Whatever his intentions, Zehaf-Bibeau's plans were thwarted after the federal authorities refused to grant him travel documents as he was on a "high-risk traveller" list. And then on Thursday, he brought terror to the heart of Canada's democracy.
