system
Given the following post, respond as if you're commenting on Reddit:
human
[General Sci-Fi] If a Immortal man committed a crime and was given a life sentence, how long would they have to serve?

So an Immortal man committed a crime and was sentenced to life in prison without parole, how long would he be locked up?

He can't die of old age and there isn't a possibility of the death sentence or another inmate attacking him so what happens to him. Does he serve the time to the age of a average man? Do they keep him imprisoned for 100 years and decide that counts as a life sentence? Or do they keep him locked up for eternity as he's Immortal and will never die in prison? 

I know this isn't strictly science fiction and more of a somewhat moral question but I'm really interested to know what the rules would be surrounding someone who doesn't die.
gpt
A 'Life Sentence' is not a uniform legal punishment. In some regions, it's literally the rest of your life, in others, it's anything above a particular amount of time (as low as 25 years). The former is apparently becomming less and less common, and only seems to exist in a few state in America.

So, in most places, a 'Life Sentence' constitutes a set term, say, 80 years, which makes it unlikely that the convicted party will every be released. In those circumstances, immortality would make it so you could functionally live put your sentence and then get released.

In the few alternatives... Well, you'd probably outlive the justice system. 

Immortality means you can basically outlive anything but other immortals, and the Universe.