Aaron Driver first came to the attention of Canadian officials in late 2014 after he voiced support for Islamic State on social media. In 2015, the Muslim convert was arrested for communicating with militants involved with attack plots in Texas and Australia. Early this year, he agreed to a court order known as a peace bond that restricted his online and cell phone use.

Yet it took a tip from the U.S. Federal Bureau of Investigation to alert Canadian intelligence officials to what police say was an imminent attack Driver was planning on a major Canadian city.

Driver, 24, died after he detonated an explosive device in the backseat of a taxi as police closed in and opened fire, the Royal Canadian Mounted Police (RCMP) said in Ottawa.

The RCMP said Driver, one of only two Canadians currently subject to a peace bond, was not under constant surveillance before the tip from the FBI came on Wednesday morning.

Driver's father, Wayne Driver, was among those left with questions about why authorities did not intervene more decisively earlier. He said he wished his son had been forced into a de-radicalization program.

"I don't think [the peace bond] was very effective at all. I mean, look at the outcome," Driver's father told the Canadian Broadcasting Corp.

"Why wasn't he on some kind of parole where he had to report a couple times a month instead of never?"

RCMP Deputy Commissioner Mike Cabana said law enforcement has difficulties both in Canada and abroad in collecting admissible evidence in anti-terrorism investigations. Even when, as in Driver's case, there is enough evidence for a court-ordered terror-related peace bond, he said the tool can not really prevent an attack.

"Our ability to monitor people 24 hours a day and 7 days a week simply does not exist. We can't do that," Cabana told reporters at a news conference in Ottawa.

With Driver's death, one Canadian resident remains under a terror-related federal peace bond, according to the Public Prosecution Service of Canada. Nine more such orders are pending, nine have already expired, and three applications for peace bonds have been withdrawn, PPSC spokeswoman Elizabeth Armitage told Reuters.

The peace bond, a type of restraining order issued by a provincial judge, can have many conditions and lasts 12 months. Driver's order required him, among other things, to get permission before purchasing a cell phone, stay off social media websites and refrain from communications with members of Islamic State and other radical groups.

In the wake of Driver's foiled attack, Public Safety Minister Ralph Goodale acknowledged that peace bonds have limits.

"Those issues will obviously need to be very carefully scrutinized," he said in an interview with CBC.

Current and former intelligence officials have said it can take dozens of people to properly track one suspect, and one said it was not surprising that the ultimate tip came from the FBI, given their vastly superior monitoring abilities.

While some 600 RCMP officers and staff were transferred from organized crime, drug and financial integrity files to the counter-terrorism beat in recent years, critics of Prime Minister Justin Trudeau's new Liberal government have argued that not enough money is being spent to fight terrorism.

The 2016 budget provided C$35-million over five years to combat radicalization, but little in the way of new funding for the RCMP or the Canadian Security and Intelligence Service (CSIS).

Trudeau was elected in October 2015 pledging to end Canada's combat role against Islamic State and roll back some of the security powers his Conservative Party predecessor had implemented.

Ray Boisvert, a former assistant director of intelligence at CSIS, said Driver was likely on an increasingly long list of so-called "B-listers" - people known to law enforcement, but considered lower risk than others and not followed regularly.

"The problem today, of course is that a target can go from mildly radicalized to highly 'weaponized' in a matter of weeks - or sooner," Boisvert, who left CSIS in 2012 and is now a security consultant to private firms, said in an email.

Mubin Shaikh, a former undercover operative with CSIS, told Reuters he considered Driver a threat back in 2015, in part because he was a Muslim convert.

"That's a red flag," he said on Thursday.

In October 2014, a Canadian Muslim convert shot and killed a soldier at Ottawa's national war memorial before launching an attack on the Canadian Parliament. The same week, another convert ran down two soldiers in Quebec, killing one.

Shaikh, now a Canadian counter-terrorism and national security consultant, said law enforcement officers walk a fine line in determining which Islamic State sympathizers are just talkers, and which represent an actual threat to Canada.

"You don't know who is going to be the one guy who is not just talking but may take action," he said. "It's better to assume that they are going to be a threat."