I disagree. How difficult would it have been to mobilize and have armed personnel at each building for the dual purpose of perp identification and capture, and to protect students [in what initially seemed remote] against the possibility that a fleeing armed felon having already displayed the capacity for murder to inflict future harm.
Certainly, one should withold judgment and refrain from casting blame while the bodies have yet to be buried and all facts made known. However, we who labor here and triangulate every which way pose these questions in search of answers.
There are over 100 buildings on the main campus. If each building had maybe 6 exits, that would require 600 police or security personnel. To answer your question “How difficult would it have been to mobilize and have armed personnel at each building” I would say pretty darn hard.
The campus has over 200 buildings. I doubt the campus police force has more than 50 total officers, not all of whom were on duty on duty at the time.