oxy moron

If you've been following the news at all you know that the Supreme Court has asked the states to suspend the death penalty until they figure out how procedures can be changed to ensure that it is administered in a way that does not constitute cruel and unusual punishment. Here's what I want to know:

How is killing someone not cruel?

It seems a little oxy moronic to me to say that there can be a humane way to kill someone. The death penalty does not make sense to me on so many levels (ethical most of all).