When law enforcement officers arrive at an active shooter incident their first priority is to?

1) Make a perimeter that won't allow the shooters to escape.

2)Save any hostages or civilians in the line of fire.

The actual reactions can vary a little, as in if there is no hostages, once the perimeter is set up, if they won't surrender they might gas them. The next priority would be to end the conflict with as little bullets and blood as possible.