I don't think the police fired first. I think they were caught flat footed because they were sitting in their vehicles.
I don’t believe they were simultaneously caught flat footed sitting in their vehicles AND in position and ready to go with high-powered rifles when the shooting started.
It’s one or the other and given the high-powered rifle thing actually took place I have a hard time even entertaining the ‘sitting in their vehicles’ proposition. It’s just not possible.
I don’t think they fired first either.
I do think they fired on people with lawful weapons carried for self defense who were seeking cover and not shooting at anyone.
After the fact somebody realized that the whole “shoot ‘em all and let God sort it out” thing wasn’t going to go down well with the public. Thus they arrested everyone with a smartphone.
Cameras from businesses are more problematic. Well run businesses have off site monitoring so that thieves can’t steal the security footage.