Does this guy sniff glue?
Why the hell would one, knowing that a criminal shooter is carrying a fully loaded gun and emptying it on civilians, would roam around and record where the shooter is instead evacuating the area and calling 911 afterwards? There is absolutely no point in recording the shooter to gather evidence, since they are plenty surveillance cameras and tons of eye witnesses. The most reasonable thing to do in that situation is escape to an area where you're no longer in danger and, if hadn't done so already, calling the police and dialing 911.