The police shooting of a knife-wielding man on a Toronto streetcar has stirred a national debate over whether the amount of force — nine shots rang out in 13 seconds — was appropriate.

Amateur videos circulating of Sammy Yatim's death over the weekend have been parsed by the public and experts, but many questions remain as Ontario's police watchdog, the Special Investigations Unit, looks into the case.

Use of force is a rare and unique permission that police are granted by society to help maintain law and order, but what are officers taught about this responsibility?

Sgt. Brad Fawcett is a trainer at the Justice Institute of B.C. where all municipal police recruits in the province are educated, and he also holds the title of provincial use-of-force coordinator. In an interview with CBC News, he walked through the training officers receive on use of force and the issues police encounter.

Use-of-force training

Fawcett estimates that use-of-force training takes up about 20 per cent of an officer's education.

"It may not sound like a lot," he notes, "but all the studies show that use of force by police accounts for less than one per cent of all the interactions that they're going to have with the public."

"The overwhelming majority of – over 99 per cent of calls – they're going to resolve just by showing up and talking to people," he said.

While at the police academy, officers are educated on a wide range of use of force issues:

- Provincial standards.

- Legal issues.

- Physiological and psychological cues to watch for.

- The national framework on use-of-force, which details the stages of police response in threatening situations.

Hands-on training also involves empty-hand tactics and how to use various weapons — from pepper spray to firearms. Municipal officers are also typically required to take refresher courses on firearms in some provinces on an annual basis depending on provincial requirements.

Fawcett says he puts a lot of emphasis on communication tactics aimed at de-escalating a situation or preventing it from becoming too volatile.

Threatening signs officers look for

An average person may not notice the signs of a person in flight-or-fight mode, but an officer is trained to be tuned into subtle physical clues of imminent danger, says Fawcett.

Among the signs are the jaw muscle balling up and the person's eyes darting around. Another clue is the clenching and unclenching of hands, because in flight-or-fight mode the extremities start to feel cold as blood rushes to major muscles.

"Police officers are seeing threat cues where other people might be looking at something and they don't see anything. And then they can't understand well, why did an officer do this?" said Fawcett.

"It's no different than a firefighter looking at the colour of smoke," he added. "It doesn't mean something to anyone else, but to the firefighter it means something important."

Increasing use of video

"We've been telling [officers] for 25 years: You can't walk a block without being captured about eight times just on store security video in downtown video. They're always going to be on film. Certainly, we want them to look good and sound better.

But at the end of the day, no use of force is going to look sterile. It's never going to look pretty. If you go into an operating theatre there's a reason the walls are stainless steel or tile up to five feet and there's a drain in the middle of the floor. After the surgery is over, they bring everything out of the room and they literally hose it down.

"Surgery isn't pretty. Use of force isn't pretty. The question is was it necessary and reasonable?"

Legal aspects of lethal force

"We teach what courts have said, when it's appropriate to use force," said Fawcett. "The courts have laid down pretty reasonable rules when it comes to the use of deadly force."

"When it comes to making a decision about the reasonableness of use of force, essentially what the courts have said is you have to be a doppelganger or a ghost in the shoes of the officer and see what they saw, not what the video camera showed, not what another witness saw.

"What was the perception of the officer and was that perception reasonable? And of course what the courts have also said [is that] you can't expect cool reflection in the face of an uplifted knife."

Public perception

"It's part of the Hollywood factor, I guess, that we have to deal with: People just think that we can Steven Seagal guns and knives out of people's hands, and that's just not the way it is," said Fawcett.

Fawcett notes that few people realize how quickly a life-or-death decision must be made.

"Time and distance is something that few people appreciate," said Fawcett. "If you're going 10 miles an hour, that's 15 feet per second. Ten miles an hour is a jog. So if somebody's 15 feet away with a knife in their hand, you have less than a second to deal with it. But most people look at the headline and go, 'Oh, the person was 20 feet away. Ohmigod, why didn't the officers do something else?'"

"The other thing to remember is we train average people [to be police officers]. We train your sister, brother husband, mother, father. They don't come with 33 years of martial arts experience.

"Some of them haven't seen a real gun until they get into policing. Some of them have never even tasted their own blood because someone punched them in the mouth."

Use of firearms by officers

"The number of shots is no barometer of whether something was reasonable or unreasonable. It sounds flippant, but if there were 10 shots fired perhaps nine weren't enough and 11 would have been too many," said Fawcett.

"Without knowing what the person was doing, you really can't say. You also have to ask why the police were there in the first place.

- Streetcar shooting probe: watchdog says police co-operation rare

- Knife-wielding Yatim told people to stay on streetcar, witness says

"People look at outcome. If you watched the whole movie and you know how the movie ends, it's very easy to see the foreshadowing. You have to remember that the officers in this movie didn't know how it was going to end ... while there may have been moments where they might have interceded differently and changed the outcome, they didn't know how the movie was going to end.

"The other thing to remember is that bullets disappear in bodies. You don't get sprays of blood like in Hollywood. You may not even know that you've hit the person because when you fire bullets into clothing you often can't see the hole. If the person's behaviour doesn't change you might not know you hit them.

"And again, you have to remember that a lot of officers never touched real guns until they were in training. It's possible that officers in these sorts of situations don't have a lot of confidence in their abilities. And the first thing they do is assume they missed."

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