Romans 6:7 says, For he who has died has been freed from sin. It's pretty easy to see that sin can't do much to a dead man, that is why it's so important we see that we were CRUCIFIED WITH Christ. By taking us into Himself at the cross, He effectively didn't just die FOR us but actually AS us - discharging us from the dominion and debt of our sin. We died with Him that day so what penalty do we have left to pay? None. Also, if Jesus dies FOR the murderer then He still leaves the murderous person a murderous person, but if he dies AS the murderer, that former murderer has died & received the full consequences of his sin and is now free to be born anew (raised) as a brand new person in Christ!!! Sin has no more sway over him because he was found guilty, tried, sentenced, and death was executed upon him in Christ. This is legally and righteously just; no smoke no mirrors. Hence Romans 6:11 says, Now reckon yourselves dead indeed to sin but alive unto God in Christ Jesus.