The RCMP say they arrested Martin Couture-Rouleau, the driver in the fatal hit-and-run attack in St-Jean-sur-Richelieu, as he was about to leave the country last summer, but didn't have evidence to charge him with any crime.​

Federal investigators had become concerned in June about the radicalization of Couture-Rouleau.

His passport was seized at that time, but he was released because investigators didn't have enough evidence to charge him.

RCMP confirmed that Martin Couture-Rouleau's passport had been seized and that he was one of 90 suspected extremists who the RCMP believed intended to join militants fighting abroad. (Martin Couture-Rouleau/Facebook)

'We could not arrest someone for having radical thoughts. It's not a crime in Canada," RCMP Supt. Martine Fontaine told a news conference Tuesday.

On Monday, Couture-Rouleau struck two members of the military with his car in a St-Jean-sur-Richelieu, Que., parking lot in what CSIS has described as "the violent expression of an extremist ideology."

One of those victims, Warrant Officer Patrice Vincent, has since died.

Couture-Rouleau was shot and killed by police following a high-speed chase as he fled the scene.

According to Quebec provincial police, Couture-Rouleau waited in the parking lot for at least two hours before he drove his car into the soldiers — one of whom was in uniform.

The parking lot in St-Jean-sur-Richelieu, located about 40 kilometres southeast of Montreal, served a number of provincial, federal and military administrative offices, as well as several commercial properties.

Quebec provincial police Lt. Guy Lapointe said a gold-beige-coloured 2000 Nissan Altima, was spotted in the parking lot as early as 9:15 a.m. Monday. The men were hit by the car at around 11:30 a.m. ET.

Victim a long-serving member of the military

The deceased victim, Vincent, 53, was a 28-year veteran of the Canadian Forces. He had been stationed at bases across Canada.

He was posted in North Bay, Ont., until 2012 as a “refrigeration and mechanical technician wing construction engineer.”

He had also served as a military firefighter. Two of his former colleagues told CBC News he was a quiet man who loved cycling and largely kept to himself.

"He was very friendly, very compassionate individual," said Dwayne MacIntosh, who worked with Vincent for three years on HMCS St John’s.

"He would do everything for you and always went out of his way."

Suspect was 'radicalized': police

The RCMP said they suspected Couture-Rouleau had become radicalized after converting to Islam.

Patrice Vincent, 53, served with the Canadian Forces for 28 years. (Department of National Defence)

They intervened in July when he attempted to leave the country to travel to Turkey.

"We did not have enough evidence to charge him and to detain him," the RCMP's Fontaine told the news conference Tuesday.

She said investigators followed up with his family and the imam at his local mosque, but had no reason to think or evidence to show that he would commit a crime on Canadian soil.

The last time police spoke with him was earlier this month.

Couture-Rouleau was one of 90 people being monitored by the RCMP as part of 63 national security investigations, RCMP Commissioner Bob Paulson said Tuesday.

Those numbers refer to people suspected of being involved with terrorism-related activities, including financing, not specifically to fighting alongside extremists.

Converted to Islam in 2013

So far, little is known about Couture-Rouleau. He had a pressure-washing business registered in Quebec. Legal documents show he converted to Islam in 2013.

Radio-Canada reported that Couture-Rouleau's Facebook page, which is no longer active, identified him as Ahmad LeConverti (Ahmad the Converted). That Facebook page shows a young man whose views had become more and more extreme over time.

Propaganda videos and other materials admiring jihad — or “holy war” against enemies of Islam — appeared on his Facebook profile page, including a video featuring the logo for the Islamic State of Iraq and Syria (ISIS).

Earlier this fall, an ISIS propaganda video called on the group’s followers to target people in a number of countries, including Canada.

It specifically suggested running people over with cars.

Gilles Rouleau, the suspect's father, refused an interview request from CBC Radio-Canada, saying he wanted to mourn his son’s death in peace.

“I lost my son. My son was everywhere [in the media] this morning. Leave me alone, I have no comment,” the father said.