In other words, he has a right to work towards redemption.
He can study necromancy for the rest of his life, and attempt to raise his victim from the grave. That’s his right. If he accomplishes it, we can talk about clemency.
His right to seek redemption isn’t being infringed upon by locking him up permanently. It is the permanence of the death he caused that is denying him redemption.
They definitely don’t want those troops coming back home and talking about their time in the west.