Once again you have solved the world's dilemmas in one single post! I am truly humbled!
Yeah right.
Here's a longer post on the subject of mercy that I found a few months after 9/11. It is not related straight to the death penalty, nor is it specifically Christian (I think they are Unitarians), but is a good work nevertheless.
What Does God Require of You?
http://www.firstparish.org/sermons/2001-12-16.html
Who is the source of mercy?
Is there nobody in Hell?
Does "mercy" then mean "no ultimate punishment if the judge is merciful"?