What you said implies that any person that has committed a violent crime remains a danger to other people, forever - and should also be punished, forever.
This is what the American justice system is like.
In a saner world, (only) people who are a danger to others would be separated from the society, and being set free would be and indication that you are no longer a danger.
In the US, being released from prison signals you are more dangerous than if you got away with your crime.
They’ve likely also noticed that the time they spent in the funhouse afterwards was not so fun after all. So even if this were true (which I don’t think it is), they might think twice about going at it again.
If someone is more likely to do it again because they are mentally unstable, they shouldn’t be released.
It may be that it's not a criteria for not hiring them, but never-the-less something you want to keep an eye one once you do. And perhaps something you want to ask them about at interview.
I dunno, it takes a lot more than a fistfight to get put in prison for violent offense. Sure people can change but only a solid work history or trusted recommendation can give you any real confidence. You may have to fire this person, or they may have to report to an abusive manage for some period of time. Some offenses are difficult to walk away from untainted.
The summer after I graduated from HS a kid I knew got into a fist fight in the parking lot of a bar. He was punched once and he went down and cracked his skull on the curb and died.
The person who hit him was charged with manslaughter.
This is what the American justice system is like.
In a saner world, (only) people who are a danger to others would be separated from the society, and being set free would be and indication that you are no longer a danger.
In the US, being released from prison signals you are more dangerous than if you got away with your crime.