I don't think the Death Penalty can be considered a 'cruel and unusual punishment'. It has a reason, so it's not unusual. But the thing is, why do it?
Isn't life in prison already a death sentence? If they're going to die anyway, why bother killing them now?
And don't say because they can escape, why would they want to escape? Freedom isn't really an option if your a wanted criminal. All you can do once you escape is either hide in poverty or get caught again.