Was the Uvalde shooting purposefully ALLOWED to happen?

Police equipped with ARs and ballistic shields were in the hallways of Robb Elementary School and told to stand down an hour before the shooting was ended. To top that, they detained anyone trying to stop the shooting. That included another police officer responding to a phone call from his dying wife, who they detained and disarmed. This doesn’t sound like incompetence. It sounds like people making sure something wasn’t interrupted.