For anyone living in the US according to your legal system, what will be his penalty?

Frankly, I hope he serves the best penalty for taking a life he never gave, despite the contradicting political opinions he didn't deserve to be killed, from what i watched about Kirk, he never threatened anybody during those political discussions to believe only in his own policy.

I feel sad for the family, the only way the family can seek comfort is knowing that the killer is facing the right punishment but it still won't bring back the deceased.