Han wrote:

At the time, possession of the firearm may have been illegal or not.
I don't know whther that vet had a license. However, disabled as he
was, he managed to enter the hospital in his wheelchair with the gun
because there was NO weapons screening at the time as there is now.
He proceeded to find the doctor and just shot him. As if it were an
ambush of sorts.

I think that answers all your questions.

If arming personnel were the answer, the only result would have been
more deaths in this case.

That, you cannot know.