You can expect a cop to run towards danger and use all available opportunities to avoid detection and try to slip up on the perpetrator unnoticed and take him out.
Why do so many act like the cop should almost challenge the shooter to a shootout at 100 paces? A school building would have offered many ways for a cop to move in undetected on a shooter occupied with hunting down victims.
If he had just starting firing randomly into the air that could have helped.