Can anyone link to the harassment/threats he mentions? (Mostly the latter, I'm sure there was much harassment but I have yet to see any real "threats").
I would suspect a lot of the harassment/threats was through things like e-mail, etc. Given the wide range of emotions this has prompted all over the place, I can find it believable that some people might send what could be construed as threatening messages, especially anonymously.
Human reactions under dangers like this are extremely unpredictable. I mean, who has ever really had a chance to test the effectiveness or wisdom of their fight or flight response?
If there is a gunman I think you would want students spread out among their classrooms. If there's a major panic there can be deaths from the panic not to mention the danger of a gunman in a hallway as students try to escape.