Sammy Yatim
© CBCMany questions remain surrounding the fatal police shooting of 18-year-old Sammy Yatim on a Toronto streetcar.
While demonstrators protest the weekend shooting of Sammy Yatim on a Toronto streetcar, questions remain about the sequence of events that led police to use deadly force to neutralize a suspect armed only with a knife.

Yatim was killed on a streetcar in Toronto's west end just after midnight ET Saturday. Much of the incident was captured on amateur video.

What we do know is that the entire incident transpired in about 10 minutes. Just after midnight, Yatim reportedly stood up and brandished a knife on the 505 streetcar on Dundas Street West near Trinity Bellwoods Park.

A few minutes later, police arrived at the scene. At that point, Yatim was alone on the stationary streetcar. A standoff quickly ensued, and within the space of 13 seconds one officer had fired nine shots.

Yatim was given CPR at the scene and then taken to hospital, where he was declared dead.

Here's a look at some of the unanswered questions...

1. What exactly happened on the streetcar prior to the police being called?

In addition to the fact that he was carrying a knife, there have been reports that Yatim exposed himself to fellow riders before ordering them and the driver off the streetcar.

2. Who called the cops?

It's unclear who alerted the police and when - was it a passenger, the driver, a witness on the street? Whoever it was, the first police responders arrived at the scene within a minute or two.

3. Why didn't the police keep him isolated on the empty streetcar?

As soon as the police arrived, there was a standoff - Yatim at the front of the streetcar, visible through the front door, exchanging strong words with several officers standing just outside the car.

Yatim, showing a knife, was the only person on the streetcar at this point. Some commentators have suggested that police could have barricaded Yatim in the streetcar until he had calmed down.

4. Why would police resort to a gun if all Yatim had was a knife?

During the standoff, officers yelled several times for Yatim to "drop the knife." At one point in the amateur video of the incident, an officer can be heard saying, "If you take one step in this direction now, that's it for you."

There were 22 officers on the scene - as one newspaper columnist noted, "more than enough, it would seem at first blush, to contain a man with a knife."

5. Why was he shot at nine times?

When it appeared as though Yatim would not comply with the police order to drop the knife, one officer fired three gunshots in quick succession, followed by a five-second pause and then six more shots.

Ross McLean, a security expert and former Toronto police officer, noted the change in posture of the shooting officer after he had discharged the first three shots. The officer's arms had come down from their initial upright shooting position to a more relaxed shooting position, which suggests that Yatim had been felled by the first three shots and that with the second barrage of shots, the officer was shooting closer to the floor of the streetcar.

6. Why did one cop do all the shooting?

Only one officer appeared to be pointing a gun at Yatim, and it was this same officer who discharged all nine shots.

The officer, whose name has not been released, has been suspended with pay.

7. Why was Yatim Tased after the fact?

An enhanced version of the video reveals that one of the officers gave Yatim a six-second jolt from a Taser after he had been shot, McLean said.

"Should you be Tasering someone who's been shot six or nine times and lying on the ground?" he told CBC News.

Reports suggest that no one had a Taser at the ready when the standoff began. McLean says if police had waited for an officer with the Taser to arrive instead of opening fire, Yatim might still be alive.