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.