"I think punishment by putting someone in a 3-by-6 cell is a lot greater than if you snuff out their life in a few seconds with a lethal injection."

It seems he wants him to suffer longer.

People are complicated and can have opposing views on what should be essentially the same thing. For example, I find it curious that someone could be opposed against abortion but support the death penalty. I also know people who claim to be against gun control because it violates their constitutional rights but who also have no problem with the government's unconstitutional surveillance programs.