It's the usual desperate need to see the black guy as the Hulking, drug-fueled brute that was, in the end, responsible for it's own death.
Emphasis on the pronouns used - part of this desperate fear is the view of black people as innately subhuman. That's why I don't engage with that sort of garbage - I personally feel no need to argue my own humanity with internet dimwits and white supremacists, any more than I feel any further need to argue with a Black Hebrew Israelite or any other bigot who spends his free time yelling on street corners. Feel free if you want to, of course. Just be warned, their worldview demands they believe it no matter the cost to themselves.