cyberdad wrote:
ISIS?
Possible, though it sorta isn't their thing going solely after a hard target, and also surrendering. I did read they released a memo saying to avoid targeting minorities in the US, so..., you could angle it in a way that would be beneficial for them without mass civilian causalities (police are civilians, but that's beside the point).
Whomever they are, they planned for something in advance, and it was sprung at a specific time with specific targets in a specific location, perhaps all within a couple of days of improvisation (if the rally wasn't known beforehand).
I'd bet on disgruntled blacks (ex .mil), possibly members of a black supremacist group in that area.