OTTAWA—One of the most dramatic Canadian national security cases in recent memory — ending with the shooting of a bomb-carrying terrorism suspect on his way to a shopping mall — was obstructed for more than a year by unbreakable encryption, RCMP officials revealed in a detailed briefing to the Toronto Star and the CBC.

Investigators had had suspicions of terrorist activity by 24-year-old Daesh supporter Aaron Driver since December 2014. But they couldn’t gather enough evidence.

“Hindsight would say that he was obviously farther along in preparing,” said Jeff Adam, the RCMP’s director general in charge of technical investigations services.

In the end, it was the last-minute tip of an “imminent” threat from the FBI — it had spotted Driver’s martyrdom video — that foiled what might have been a mass killing.

The tip came as Driver was preparing homemade explosives for a suicide bombing mission later that day. Police shot and killed Driver outside his home in Strathroy, Ont., in August, just as he entered a cab to head to a shopping area in downtown London, Ont.

Contrary to what was reported at the time, the explosive device Driver carried was deadly.

Full detonation in a public place would have caused “death and grievous bodily harm,” Adam said.

An analysis of the bomb, obtained by the Star and CBC, shows that anyone within 2.1 metres (about seven feet) of the detonation would have faced death or serious injury, not including the impact of shrapnel “fragmentation.”

Driver had embedded 139 ball bearings in the device that would have added to the carnage, the Star/CBC investigation has learned.

The device did partially detonate in the taxi. But it was only a small portion of the much larger explosive, police confirmed.

Driver, seen in media images wearing a black balaclava, was the son of a Canadian Forces corporal. He converted to Islam in his early 20s and praised terrorist activities in social media posts, including the attack on Parliament Hill by Michael Zehaf-Bibeau in October 2014.

Driver came close to succeeding by exploiting what police call “going dark” — the disappearance of evidence behind sophisticated digital privacy.

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He first appeared on the RCMP’s radar in December 2014 when communicating online with terrorist suspects and “prominent” Daesh sympathizers, including suspects associated with attacks in Texas and Australia.

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Police took a hands-off approach because Driver’s personal communications were encrypted, RCMP officials said. Investigators knew who he was talking to, but could never crack the content of their messages.

Driver was arrested in June 2015 on suspicion that he might participate in the “activity of a terrorist group” or “carry out a terrorist activity.” But without sufficient evidence, he was placed under a peace bond and released.

“We had significant and reasonable probable grounds to believe there are concerns with this individual,” Adam said. “The fact that he was out and available to do that is probably because we could not break the encrypted communications. And that’s going dark.”