I think the first scenario is pretty unrealistic - some guy is casing cars and stashes a gun behind a car and then comes out firing? I think that one is set up to "kill" the cop so then the trainee is trigger happy in the next scenario so he "shoots" the unarmed man approaching him aggressively.
I agree with this.
You can absolutely set-up scenarios where cops get killed without any recourse, AND where they kill innocent people. The same is true of non-cops too. If someone has a modicum of intelligence and really wants to shoot you, you're going to get shot.
Having said that, I think the Michael Brown shooting was Brown's own fault since he apparently did physically attack an officer, for the same reasons.
However, there are other scenarios where police have physical control of someone, the person is restrained or has been patted down, and the cops use excessive force on them due to either adrenaline or machismo. This is what happened to Eric Garner. Strangleholds are banned in arresting procedures for exactly that reason. The officer is full of adrenaline and has no idea if he should let go or not. That incident was the fault of the arresting officer.
Similarly, if you're NOT an officer at all, you need to be aware of your own behavior and whether it's threatening someone else. This is what happened in the Trayvon Martin situation. The profiling in that case, and the "thug-based" character assassination that followed, is where the "race divide" creeps in.
Having said that, I like to know when the police kill unarmed people of all colors, to be able to follow how many incidents there are and really weight how much race seems to effect it (for example, if Trayvon Martin and Eric Garner had been doing the same things and were white girls, I doubt they'd be dead). Likewise, I'd like to see how many police are actually abruptly murdered by people in the manner they show in the "training scenario," such as what happened to the two New York cops, in order to see how likely that occurs also. Those would be important to know for both the public and the cops when deciding whether to use weapons in a situation, and what weapons to use.