I live in a bad neighborhood where gunshots are common. Since I've lived here there have probably been dozens of homicides within a .5 mile radius. Living here has changed my perception of officer involved shootings.
People don't realize how quickly things go from a slightly weird situation to bullets in the air. It goes from somebody standing funny, maybe they have a hand behind their back or they're holding a towel in a weird way, then bullets. Fast. A quarter of a second separates "that's weird" from "oh no somebody's shooting."
If you've ever dropped your phone and had to figure out what to do before it hits the ground that's about as much time as police have to make these life-and-death decisions.
In this particular situation, the police believed they were arriving to a hostage situation where somebody had already been killed.
What happened is tragic. If you've ever dug into this story it's heartbreaking. At the same time I don't think the anger at police lines up with what happened here at all.