The answer: Alzheimer's disease can cause paranoia and violent outbursts in the elderly, but it could also be paranoid Schizophrenia. And if he is Vietnamese, he might have PTSS and a lot of anger if he had to flee the communists.
some drugs cause extreme paranoia too- coke, meth etc- i know he was 72, but there are elderly folks who are drug addicts too- not saying he was- but it’s one possibility- not sure if some medications can cause paranoia or not? but might be another possibility