The tone of the article suggests that the killer was roaming the building at will for an indefinite length of time, killing left and right, while the cops huddled outside. That doesn’t seem accurate — it seems more like that he was contained to the room he took over initially, and the police had the rest of the building.
That scenario has been presented as one description of what happened. The spokesman said "They had the shooter pinned down in one room..." but that still is not an adequate response to a shooter in a school, because containing the killer in one room is not the same as preventing them from doing what they are trying to do.
And having somebody contained in an area is not the same as them being "pinned down". Far from it.
It looks like the police response was flawed, like it was in Columbine, and at the school in Florida. That's very sad and suggests more work and training is necessary so that police do respond effectively in such a situation.