The man is not reported to have repented. This he needs to do to save his soul. And even if he does, he needs to be separated from society until the day he dies. That means "life without the possibility of parole," or a just death sentence which is carried out in a way that is swift and certain.
No, even if h repents he needs to go see God, who said ‘send them to me”. Now, the only way I know how to send someone to God is to take their Mortal Life.
God IS pro death penalty.
And this is all I’m going to say on the subject