The gun fire had stopped after about 10 min.
The killer had already shot a security guard and police officer and the officers responding were not sure if the killer was still in the room or had fled and was trying to escape.
They were on the way up making sure he did not escape and made sure the floors were cleared, there were no hostages and the people in the rooms were cleared before breaching the door to the killers room.
Things would have been much different if the killer was still shooting at people on the ground.
The police did exactly the right thing.
Can you provide a source for your assertion?