It is easy to criticize the police, but there was one shooter, and only 19 police officers. Surely they were not competent enough to stop him?

I don't understand how several kids called 911 over nearly an hours time and some cops were inside the school's hallway waiting yet the commanding officer claims that he did not think that it was an active shooter situation?
Why wasn't he on the scene himself ASAP?
Who was in charge of relaying the facts to him?
They say that info from the 911 calls possibly wasn't getting to the cops. Why?
Just nonsense