Here is a link to the Wiki listing:
https://en.wikipedia.org/wiki/University_of_Texas_Tower_Shooting
I wanted to read about the brave civilian who helped. His name was Crum and he was a retired tail gunner in the air force. I suspected he was a retired military man.
Whitman, an ex marine, was a pretty good shot with the sniper rifle. I can imagine that shooting from such a tall place was not easy. He must have known how to adjust his sights (it had a scope) as he immediately began to make precise shots.
He killed one fellow at 500 yards and hit another non fatally at I believe it was 1500 yards, nearly a mile away.
His autopsy revealed a small tumor in his brain which may have caused him to go off.
The incident changed how police departments were equipped going forward. Portable radios, vests and sniper capabilities became standard parts of police departments not long after this incident.
the tower was limited in its access and eventually closed to the public.
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.

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..I also have a 427 Cobra replica with an aluminum chassis.