This guy had absolutely nothing to do with why the officers were chasing a suspect through an apartment complex. For whatever reason, he decided to get involved and shoot one of the officers.
The true point of sharing this video is to demonstrate how quickly this officer needed to react, as well as the continuous reminder to be aware of everything that is going on around us.
Give the officer some serious credit here. The way he was able to react, while on a foot chase for someone else, is seriously amazing.