The reality of the availability bias isn't in question, it's whether or not people's belief about police brutality is accurate and if not, why it isn't. Sure, the AB is real. It MAY be a factor in why people think black people are killed in proportionally higher numbers than people of other races, but what's relevant is whether or not it's actually happening.
Availability: A heuristic for judging frequency and probability
edit:
> The reality of the availability bias isn't in question, it's whether or not people's belief about police brutality is accurate
It would be nice to have some objective evidence showing why this example is a special case immune to availability bias.