Apparently they had received multiple calls from children inside, who told of the shots and dead. Granted the first was half an hour later, and the one where she mentioned dead victims being forty minutes after he entered, but why that wasn't immediately relayed to the police and for them to immediately act baffles meI'm not sure why this narrative is going around now, but it seems to me like he boarded himself up in one room and they just decided to react as though it were a hostage situation and/or that everyone inside was immediately presumed dead. So the appropriate action would be to play a waiting game.
What do I know though. Half of me feels angry about it too. Just bust in there guns blazing immediately.