I agree that 8 years is ridiculous and an embarrassment to the legal system and all parties in it. But if IIRC there is some argument about early onset dementia for this old guy. And as a defense attorney, I have always thought there was an unfortunate gap between “Not legally responsible due to mental illness” and “a guy still suffering enough from a mental disability that we don’t bring the full force of the law down on him.”
Obviously he should never own or possess a gun again, but again, IIRC, the parties keep trying to work out something to be fair. Yes, the victim is dead, but we still don’t impose worthless punishments on people who really don’t understand why they are being punished.