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"And the people who were dense on Aug. 21 are the ones who didn't realize the campus was closed, evacuated and classes locked by 9 am."
The campus was partially closed, classes were cancelled (by 10:30 am, if I remember right), but students were asked to stay in (or return to) their dorms or "academic areas." There were still many people on campus who could have been shot by a mentally ill shooter, in their dorms or in those "academic areas," if the shooter had been trying to engage in mass murder rather than trying to hide.
And, as many have said, the idea that all students on a campus are awake and reading their e-mails or checking their voicemails by 9 am is ludicrous.