This may be surprising, coming from a man who spends more on guns than on his car, but I'm absolutely against the death penalty. That's not to say that I hold the life of a convicted murder in any particular esteem, I simply don't feel that the government has the legitimate power to decide who does and does not have a right to live. Add on to that, it allows emotion to permeate in our justice system, with families of victims craving revenge. That's not what our legal system is about. Justice needs to be cold and emotionless, so that it can be even and fair.
I won't get into the details with regards to the governments use of deadly force (it's far too nuanced for a primarily ideological discussion), but in essence the primary difference between police shooting someone and a prison executing someone is that the police are acting in defense, not in punishment (brutality and corruption not withstanding). In short, once someone is arrested, they should no longer be a danger to anyone, so what is the reason to kill them?