It has been ruled MANY times that the police have NO DUTY/ Obligation/ Liability or Responsibility to protect people.
And this needs to be brought up every single time in gun control debates.
The Police are NOT there to protect You.
While I likely would have tried to sneak in and get a shot at the perp from cover, with clear and certain egress, I would not expect every sworn officer to be held to the standard of suicide.
If that is the standard my FR brethren want in LEO, they should endeavor to codify it in their state. And if successful, watch cops resign in droves.
Entry into that building would have a very, very high risk of being shot by a .223 round. Nearly certain. And nearly certain to not have affected the outcome.