I'm quite certain that the dead man was offended at being asked or directed to stop texting and things escalated from there. But, unless something a little more deadly than popcorn was thrown at the retired police captain, I suspect that he has a serious legal problem.
Police officers are trained to defuse confrontations, trained in the use of firearms, and trained in the law on use of deadly force.
Since he is retired and clearly not on duty, one of his main lines of defense will not be available to him.
I wonder how retired police captains fare in prison?
After reading post 40 I can imagine now that the 70 year old men felt threatened.
If they are in GP, and the other inmates know about it, they will get killed. I knew a few former LEOs in the joint, during my career. Otherwise, they are in PC, or walk alone facilities, designed to protect them from the other criminals.