I think the difference be between Briana's and George's killing and why one got the limelight was two fold. One could have maybe explained away as an honest mistake or a bad situation. The other was pretty blatant malice. George being the latter.
Outrage takes time to build and can dissipate quickly. It maybe the public had just reached a tipping point after months and years of unlawful killing by police of black people, mostly male, mostly young.
I think the offense people took with your reply is due to the historic "he was no Angel" excuse. As a way to justify the inexcusable, cold blooded murder.