If you haven't seen the body cam video of the police shooting of Daniel Shaver, I encourage you not to -- it's really disturbing. There are so many things wrong with it, but I guess since race is not a potential issue (the victim was white) it hasn't received as much attention as some other shootings.
There are things to be said on both sides, and my opinion varies depending on the case. I thought the shooting of Philando Castile earlier this year was inexcusable; in other cases, police officers have had at least some reason for pulling the trigger quickly.
It is very tricky to judge a shooting on its merits, even when captured on video. We (and juries) have to do it, of course, and we are right to make decisions for and against policemen for their actions, but it doesn't seem to me like we are going to make fundamental changes by jailing this or that cop for unjustified homicide. (That said, after the Castile and Shaver "not guilty" verdicts, I have to wonder what it takes for an officer to be convicted.)
What I would really like to know is why policemen are going into situations with the attitude that they subject is likely to kill them, even when there is no evidence to that effect. In Castile's case, it was a routine traffic stop and Castile was behaving with all due deference to the police officer. In Shaver's case, the officer was responding to a call that someone was armed with a rifle and pointing it at someone, but you would think that fear of a dangerous killer would have been almost completely mitigated when the guy appeared outside his hotel door without a rifle and complied with the officer's instructions to put himself in a particularly defenseless position on the floor. Officers are not supposed to profile based on skin colour, but what about behaviour? What kind of violent, cold-blooded cop killer would go through that ordeal, which was humiliating and gave all the advantages to the policemen? In Castile's case, what kind of killer would announce that he had a concealed weapon if he intended to use it?
The inexplicable thing is the way some officers seem to be going into every interaction with every citizen as though his own life were at risk. The call that resulted in Shaver's death was not about a dangerous criminal who had shot or threatened to shoot someone, but a call from a hotel front desk employee who had received a call from another guest that he had seen someone with a rifle. In other words, it was at least third-hand information by the time it got to police, and in any case they had no independent confirmation that there was anything wrong.
This is like the cases of "swatting" in which a 911 emergency call gets the police to dispatch a SWAT team to someone's residence, which has (predictably) led to confusion and occasional deaths. Why in the world would the police send a SWAT team on the basis of an anonymous call? SWAT should only be called in, I would think, in cases where there was a known (i.e. verified by at least one police officer) armed and dangerous (i.e. known to have shot or attempted to shoot, or at least threatened to shoot, one or more people) person to deal with. Responding to rumours with a SWAT team is an invitation to tragedy (as the anonymous callers no doubt intend).
Maybe I'm wrong, but I had the impression that policemen often respond to situations in which someone is excited beyond reasonable bounds. Situations in which someone might be screaming or crying and worried for his or her life. I had also assumed that officers routinely responded to such calls by proceeding, as cautiously as necessary, to investigate, trying to keep the situation as calm as possible. Their goal is to get everyone to take a deep breath and stop any violence before it occurs.
The Shaver situation was handled in just the opposite way. The police overreacted from the beginning, treating Shaver (who was not doing anything illegal to begin with) as a mortal threat. If you treat someone that way, and assume that every action he takes might be intended to end your life, obviously you are going to shoot him sometimes when he is not intending any harm. The Castile traffic stop started out more routine, but the officer was obviously willing to assume the worst without the slightest indication.
We have to train our police better. They have to approach situations calmly, intending to defuse them; not nervously, ready to escalate at the smallest movements unless there is some other reason to treat the subject as a likely dangerous one. And for officers who are naturally nervous -- they need to be assigned desk work. No one who could interpret Shaver's actions as threatening should ever be doing that kind of job.