Just as an aside as I have read numerous times in this thread that these are instances where regular folk would be arrested and charged, the fact is that in Canada, police are protected or otherwise provided different standards when using force.
This is entrenched in the Criminal Code section 25 which states:
Protection of persons acting under authority
25 (1) Every one who is required or authorized by law to do anything in the administration or enforcement of the law
(a) as a private person,
(b) as a peace officer or public officer,
(c) in aid of a peace officer or public officer, or
(d) by virtue of his office,
is, if he acts on reasonable grounds, justified in doing what he is required or authorized to do and in using as much force as is necessary for that purpose.
This includes the use of deadly force.
This is why these cases are so complex and why it requires extensive consideration beyond a "regular" homicide.
Further R v Nasogaluak 2007 - Allowance must be made for the exigencies of the moment. Officer cannot be expected to measure the force used with exactitude. It is both unreasonable and unrealistic to impose an obligation on the police to employ only the least amount of force which might successfully achieve their objective. To do so would result in unnecessary danger to themselves and others. Officers are justified and exempt from liability in these situations if they use no more force than is necessary, having to regard to their reasonably held assessment of the circumstances and dangers in which they find themselves.
I am not looking to absolved anyone, just pointing out that the issue is more complex than an iphone video and speaks more to the thoughts, judgments and feelings of those involved and whether those were reasonable, necessary and proportionate.