For people like this one, I've always thought the most just punishment would be to literally erase that person. Remove all traces of their identity from the public eye, leaving the only evidence that they were ever alive in government records like birth/death certificates. Driver's license, home ownership, permits, taxes, burn it all. Give that person a numerical designation and place them in solitary confinement.
Allow the individual food, water, reading materials, exercise equipment, whatever. The individual cannot however, receive any reflective surfaces, writing utencils, recording devices, or other means of interacting with or recording the idea of "self". They can't see themselves in a mirror or write a diary. As they age, they can only remember what they once looked like, not knowing how they've changed over the decades. The only time they hear their own voice is when they speak, though they have no one to speak to. Essentially, they become a stranger to even themselves.
It's cruel, arguably far crueler than simply giving them the death penalty, but it's
not moral or ethical, but just |
just.
Edit: To all of the above, please remain civil and considerate.