Does Death Penalty Save Lives?

Does Death Penalty Save Lives? A New Debate – New York Times

This is an interesting piece about a number of recent quantitative studies which have found that, controlling for other variables,  the death penalty can save more lives than it ends.

What interests me, that is not addressed in this article, is the question of what is it about the death penalty that is saving lives?  There are so many possibilities (ranging from a number of effects from locking up harmful criminals, to the impact of the law’s expressed condemnation of murder and violent crime), all of which statistical studies might have a hard time separating out all of these variables. Also unexamined is whether there are other punishments that might have similar effects.