If he were completely without the ability to feel pain I’d doubt he’d be very successful with any remotely physical activity, so that sounds like an exaggeration. Medication can provoke neuropathy, but there’s usually a sort of nonspecific aching associated with a surface numbness that is more specific. My father had it, nerve pain but his feet were numb, difficulty walking because he couldn’t feel iiregularities beneath his feet and it affected his balance.
The security head of his high school who also advised Lanza’s extracurricular activity said he had to be watched closely because he could not feel the pain caused by fire and thus could damage himself severely. I have the same thing your dad had and don’t notice any cut or blister in my foot. Thus I inspect my feet nightly. There is some feeling but I do have issues with balance.
I was just wondering how anyone could look at young children and shoot them multiple times. Imagine the terror and pain of the child waiting to die. Empathy won’t let most of us do this. Perhaps he couldn’t imagine what they were feeling? The other reasons for such a killing frenzy (religion, race or ethnic hatred, not believing the others to be human) don’t seem to be present here.