When you chose to commit that act of sin, you're already damned and does not deserve any chances or sympathy from society. Keeping murderers in cells is a waste of tax payer's money. Why are you paying the expenses of someone who murdered someone else's daughter?
To reduce a society to fixed order, there needs to be a form of deterrence to these kind of people and the death penalty does that. Of course if they don't care about the penalty and goes ahead in committing their crimes, all the more are they unworthy of forgiveness and chances aren't they? If you think that a civilized society has no place for the death penalty, and that people in support of the penalty are heartless-coldblooded-people-who-don't-give-a-damn about-the-bible or God, that is your belief and your stand. If you are an atheist and believes in repentance or hope, then so be it. There are reasons why certain countries legalize the death penalty and why states in US doesn't. It's funny to see why western countries criticize countries like Singapore for their death penalty law and ignore muslim countries like Saudi Arabia (behaded 80 people so far in 2015).