Intentional murder is the ONE thing in Judaism that there can be NO redemption from. In any other crime, you can at least symbolically petition the victim/s for forgiveness...and even if they choose not to forgive you, you have made the attempt and are considered for redemption in the Lord’s eyes. But a person can not petition a dead victim for forgiveness and even if the victim’s family forgives you, you can never make your peace with the soul you deprived of its earthly life. THAT is what justifies the death penalty. If the death penalty is not given, it makes no difference because you WILL die someday and eternal death follow. It is the ONE thing you can never, ever escape.
You have a very different theology than I do as exposed by this issue. We probably shouldn’t pursue that conflict here.