As far as God is concerned, yes. But society still needs to be protected from dangerous people and the penal code needs to be brought up to date from the dark ages - prisoners should be productive and pay for their stay in the Big House as well as pay back those they've robbed what can be reasonably repaid.
And there you just negated your own argument.
You see when you stick people who are capable of shooting an innocent person twice and then burying her alive so she would slowly die a horrible death in jail you place everyone who is in that jail in danger.
People like that do murder again. They murder guards and other inmates. They break out and murder other innocent people who were suppose to have been protected from that dangerous person.
On the other hand there is zero danger from an executed murderer.
You argue against yourself here. The traditional penalty for murder in Jesus' time and until recently is death. That is the civil penalty. The laws requiring death in the Old Testament came from the People's demand for a civil law. The debt paid for on the cross was for the ultimate penalty, not for a civil, earthly one.
Please tell me how a murderer would pay me back for a murdered wife, child, mother, father, brother, sister or any other human being that I cared for; or for that matter some person I did not even know.
GOD gave each and every person their life to cherish, live and protect to the best of their ability; and a murderer comes along and arbitrarily steals that GOD given gift from them, for no good reason other than they can?
The person who murders steals more than just a life; they take all that a child, woman or man could have ever done or been, all their love, happiness and productivity forever.
You are starting to sound like one of those Born Again Christians sitting in a death row cell in a prison some where trying to avoid your debt to society.