I certainly can't argue with your lived experience, but I hope you'll appreciate that from my point of view it's an anecdote, even though I don't doubt your sincerity, nor the accuracy of your statement.

Few people just snap and kill somebody in under a few seconds, its the fact that they’re ever letting shit get that far in the first place is the actual core issue here. It’s incredibly easy to look at a single video and say “I would never” but part of my talent for handling these situations is understanding what causes a person to get to that point. I’m the person who notices my coworkers getting frustrated and taps them out because I’ve noticed that it’s always the martyrs who say “I would never” that fail to monitor and intervene with their own frustration levels that wind up doing the most fucked up shit.

I agree with all of this, but combined with the information in the OP, what we can do, rather than blame that cop for their own mental health struggles (although I do blame a person with those kinds of anger control issues for choosing a career where they need to decide whether to kill people or not), I think there must be, should be, and should always have been actual consequences not only for the cop who pulled the trigger, but for the folks who hired and retained him.

And if the answer is "for this reason or that they didn't have knowledge of all those details" - then THAT problem can be the first one that supposed well meaning police solve if they want to start building some faith that they actually want to solve these problems as badly as us potential targets do.

they’ll see these videos of cops killing black people and SAY ACAB or defund the police,

The post you originally replied to is the closest I've ever come to actually saying it, but although I usually refuse to even get that close, I will distill down a somewhat famous Chris Rock skit to only its punchline. I may not walk around saying ACAB, but I understand.