In a quiet row of red brick houses now cordoned off by police in this small Southern Ontario town, officials say a terror suspect was killed as the RCMP moved Wednesday to counter an alleged plot that might have been targeted at public transit in Toronto.

The lone suspect, 24-year-old Aaron Driver, was known for making social-media posts supporting the Islamic State, using aliases such as Harun Abdurahman. The estranged son of a Canadian Forces corporal, he had converted to Islam in 2008 and agreed last year to a peace bond that restricted his movements and online activities.

A federal source said Mr. Driver, who was arrested in June of last year in Winnipeg due to concerns about his activities online, was dead.

Who is Aaron Driver? What we know so far about man killed after standoff in Strathroy

The source said Mr. Driver intended to do something and had the capabilities to carry it out.

Transit agencies in Toronto confirmed that they were warned of a security threat before RCMP confronted Mr. Driver on Wednesday.

In Strathroy, residents say swarms of law enforcement descended on their small community.

Houses on either side of the Park Street residence where Mr. Driver had been staying were evacuated.

A neighbour, Irene Lee, said she was at her home close by when she heard a loud noise. She said shortly afterward, a police officer came by to tell people to stay inside their homes.

Mr. Driver’s father, Wayne, told the National Post that his son had set off a bomb and was about to detonate a second one when he was shot dead. A taxi driver was wounded in the first blast but shooting Aaron might have saved the driver’s life, the elder Mr. Driver said.

“Our worst nightmare has come true. As sad and shocked as I am, it doesn’t surprise me that it has come to this. Aaron was a good kid who went down a dark path and couldn’t find the light again,” he said.

Ms. Lee said there were up to 25 marked and unmarked cruisers outside a home on Park Street.

A sport utility vehicle, pulled halfway onto the curb, shone its lights on one house throughout the night. Neighbours identified this residence – red brick base with a white siding – as the one Mr. Driver lived in with his sister.

Neighbours said Mr. Driver worked at Meridian Lightweight Technologies Inc., a company that manufactures automotive parts using magnesium.

Earlier in the day, the RCMP said it received “credible information” about what was only described as a potential terrorist threat. The force released no other information about the nature of the threat.

On Thursday morning, a spokesman for the Toronto Transit Commission said the agency was made aware of a terror threat investigation early the previous day, but noted that it had no specifics attached.

Brad Ross said that as a precaution a “vigilance notice” was issued to all staff encouraging them to say something if they saw something of concern. He said such notices are commonly issued after security incidents around the world or if the TTC is advised of threats closer to home.

A spokeswoman for Metrolinx, the Ontario government agency which runs the Greater Toronto Area’s regional transit lines, says it was also advised of a security threat.

Anne Marie Aikins says the agency raised its level of vigilance and worked closely with national, provincial and local forces in response.

Mr. Driver grew up in Ontario but was living in Winnipeg when his Tweeting activities caught the attention of authorities.

The peace-bond conditions that he agreed to in February included living with his sister in Strathroy, Ont., as well as not possessing firearms or explosives, not possessing cellphones or computers, staying off social media and not possessing anything bearing the symbols of the Islamic State group.

In a 2015 interview with the CBC, Mr. Driver had said he was not a terrorism threat but added “I’m okay with soldiers or police officers being targeted” because of what they did to Muslims.

“Seeing some of the things that are happening in Syria, it infuriates you and it breaks your heart at the same time, and I think that if you know what’s going on, you have to do something,” he said.

“What it would take would be for the West to just stop killing Muslims, stop bombing, stop arresting Muslims, take responsibility for the crimes they’ve committed in the past and just stay at home and work on their own problems.”

Len Tailleur, Mr. Driver’s former lawyer, said he was “aghast and shocked” to learn of Wednesday’s events. Mr. Tailleur represented Mr. Driver in 2015 and early 2016, when federal authorities wanted to limit his client’s activities on suspicion that he might help or engage in terrorist activities. Mr. Driver launched a challenge under the Charter of Rights and Freedoms.

In an interview late Wednesday, Mr. Tailleur said his former client never gave any indication that he would carry out any terrorist activities.

“He was such a passive individual. He was not an aggressive person,” he said. “I had a couple assessments done of him, which I gave to the federal Department of Justice.

“Those assessments indicated there was no sociopathology, no psychiatric illnesses, any of those types of things. But there was this overriding religious conviction, which, I guess at the end of the day, was the compelling factor in his alleged latest decision to do what he did here.”

The lawyer described his former client as a “loner” and a “passive individual.”

“When he would come to court, he would be reading his Koran,” Mr. Tailleur said. “I’ll tell you right now that he was one of the best clients I ever had, because he took instructions very well and was never aggressive in my conversations with him.

“He disputed a lot of things that were alleged, about specific conclusions that CSIS or the RCMP would want to make about his behaviour, but there was absolutely nothing to indicate that he was going to be [like this].”

The Canadian Press reported that Mr. Driver, who was in his mid-20s, was first picked up by police in 2015 but released later after being ordered to comply with 18 different conditions, including wearing a GPS tracking device.

At the time, the bail conditions drew criticism from the Manitoba Association of Rights and Liberties.

“This is a person – a Canadian citizen – who has not been charged with a crime ... and yet he’s going to be subject to 24-7 GPS monitoring,” said association president Corey Shefman.

The office of former Tory public safety minister Steven Blaney defended the move, saying the government must combat terrorism.

“We will continue to ensure that our police forces have the tools they need to protect Canadians against this evolving threat of terrorism,” Mr. Blaney’s press secretary, Jeremy Laurin, wrote in an e-mail at the time.

Earlier Wednesday, the RCMP released a statement that said the force took the “proper course of action” to ensure the public was not at risk.

Federal Public Safety Minister Ralph Goodale issued a statement saying he had discussed the case with the Prime Minister “to confirm that public safety has been and continues to be properly protected.”

“There is no greater responsibility of the government than to keep its citizens safe,” he said.