A shooting by a Toronto police officer to stop a brutal and prolonged stabbing attack last week appears to be justified, says a former director of Ontario's police watchdog, based on his viewing of video of the incident that is making the rounds on social media.

The video was taken on the morning of Sept. 14 after police were called to Driftwood Avenue and Cobbler Crescent, north of Jane and Finch, around 9:15 a.m. for reports of an assault.

The two officers found one man stabbing another on the sidewalk, according to a news release from the Special Investigations Unit. One officer fired his gun and hit the attacker.

The stabbing victim, a man in his 60s, and a man in his 20s who was shot, were taken to hospital and treated for non-life-threatening injuries, the release said.

The Special Investigations Unit is investigating a stabbing attack that led one officer to shoot a man. (Mehrdad Nazarahari/CBC)

The video, posted to Facebook on Wednesday, picks up during the attack, as onlookers shout, "Can you stop?" Dogs begin barking and more onlookers appear, some driving their cars close to the two men while honking their horns, in attempts to stop the violence.

'Pretty horrible' video

On Thursday, Ian Scott, former director of the SIU, which probes incidents involving police that result in civilian injury or death, said he would like to hear an explicit warning from police before hearing the gunshot.

"But it's so clear that the level of aggression by the fellow who ends up being shot is so stark that, in my view, based solely on the video — there may be more information or more evidence — but based solely on the video, the use of force appears to be justified in these circumstances," Scott told CBC Toronto after viewing the footage.

The SIU has taken over the investigation and has asked anyone with information to contact the lead investigator at 800-787-8529. If anyone has more video of the incident it can be uploaded at the SIU website.

Scott, who saw his share of gruesome evidence during his time at the SIU, called the video "pretty horrible," and said it was "very hard" to watch that degree of violence.

While watching the clip, he said that in this instance, where the attacker is using an "extreme degree of force," both police and civilians have the right to use force, including lethal force, to try to stop the attack.

"It's not only a police officer who gets those protections under the Criminal Code," Scott said. "It's any individual."

Former SIU director Ian Scott called video of last week's stabbing and police shooting 'very hard' to watch. (Sue Goodspeed/CBC)

He would not characterize it as an open-and-shut case for the SIU, noting that there may be other videos that provide more information about what happened, as will both eyewitness interviews and forensic evidence.

It is a rare instance where video exists to show investigators so much detail about what happened in such a public incident, not to mention a police shooting. The video evidence in the Sammy Yatim case is one example.

Scott noted that video will become more prevalent in the age of smartphones and public surveillance cameras. And any video evidence helps investigators determine what type of charges, if any, should be laid.

"If I had to predict, I would say the officer is not going to be charged with any criminal offence," he said.

"That's why I have advocated body-worn cameras," he said. "Many times it's going to help the police in these circumstances."

'It's real and it happens'

It's also important for members of the public to see these videos, he said, so they can decide for themselves if the use of force is justified, but also so they can see the harrowing circumstances police can find themselves in.

"This is the reality of some of the scenarios that exist in the city," Scott said. "It's regrettable, but it's real and it happens."

Area resident Maria Pilepal said that in 10 years living in the neighbourhood she's never seen anything like the stabbing and police shooting that played out one week ago.

"It's scary," she said.

While Pilepal said she believes the shooting was justified, resident Vincent Evidente wasn't so sure.

"I don't think he should pull out his sidearm," Evidente said. "Can you imagine? He could shoot it anywhere."