This case has nothing to do with the 2A.
Given the coldblooded and ill-advised statements he made, and given his advanced age, his attorney would be much better off advising a plea deal.
While it has nothing, per se, to do with the 2nd Amendment, an attorney who is anti-2nd Amendment would not work in the man’s best interest.
He could also plead temporary insanity and claim he based his comments after the shooting that he was angry, scared, etc. and that he does not feel that way now.