I'm not assuming anything. I know that despite whatever happened in this particular case (though it would seem rare to tell a cop you have a gun and then try to shoot him with it, and then be a cop freaking out, cursing and shaking over what you have just done, and by all accounts this guy was a super stand up guy, great school employee, no rap sheet, etc, etc, etc), that despite whatever happened in this particular case we have a problem with institutionalized violence against bodies of color in the United States, especially Black males. We have a structural problem with highly militarized police that believe they are fighting a war against the people they are paid to protect. We have a problem with holding those police accountable for their actions. The whole story is a long story, starting with slavery, continuing through redlining and segregation, etc but this whole story is a story about cops that kill more people in a day in this country than other industrialized countries have in a year. It's a story about unarmed Black men being killed at disproportionate rates even while white mass shooters are brought in alive and heavily armed. It's a whole story about a lot of things actually - a prison industrial complex grown bloated, a war on drugs that doesn't work, police training that is incomplete or wrong, complacent citizens, etc.
But again, I'm not passing judgement on whether this particular killing was "justified" or not. I'm just saying we already know the whole story, and the whole story is bigger than this particular tragic ending.