How in the h-ll could they or should they have known he was going to show up in classrooms 2 hrs later and execute people. Please give it a rest.
You miss the point. No one thought that. But a murderer was loose on the campus. Typically police officers try to find the suspect while keeping nearby folks out of harms way. It's called "Shelter-in Place." And to do it successfully, you need to spread the word ASAP.