they just said that in the weeks before this happened there were a bunch of bomb threats called in that have been traced back to the shooter, they think he was doing this to watch how security reacts so this shooting was definetly premeditated and planned out. There was nothing they could have really done to prevent it.
edit: the shooter put chains on the doors the campus safety used for emergency situations, so he was definetly watching when they reacted to the bomb threats from the weeks before