Maybe the firing of the first police officer (who should be offered a position at a police academy to initiate a change in policing mentality...) was a move to legally protect the two officers who arrived later and shot the mentally impaired person? For if you grant that not shooting was the right decision in this situation how are you going to justify killing the disruptor?

Disclaimer: I am not a laywer nor do I live in the US, so this is just my personal speculation.