Tsarnaev Death Penalty

I can't say I'm surprised that  Dzhokhar Tsarnaev received the death penalty, though disappointed. In an odd ironic sense, executing someone who had expressed a desire for martyrdom (however seriously you want to take that) seems sort of counter intuitive. I know plenty of people want him to suffer, which the kind of maximum prison he would have gone to certainly would have done, but I'm not comfortable with that idea either. I do believe in serious consequences and protection of the public for heinous criminals, but I also believe it needs to be done with respect for our shared humanity, and as a Christian for the image of God in even the most despicable of us. Genesis 9:6 is sometimes quoted as divine sanction of capital punishment, but it clearly says that the image of God in our fellow humans is the basis for that, which can hardly be claimed with the way the death penalty is handled anywhere today. I also know claiming religious justification for such laws leads to horrors and would rightly not be constitutional in the US. Yet, as a Christian I must find something deeper than deterrence to justify the death penalty, which I'm afraid is just code for revenge that eats at the souls of those who harbor it.