Death Penalty working?

http://www.nytimes.com/2007/11/18/us/18deter.html?_r=2&th&emc=th&oref=slogin&oref=slogin

New studies out of Louisiana State University attempt to prove that the death penalty is statistically a deterrent for homicides, and that "For each inmate put to death, the studies say, 3 to 18 murders are prevented."
However, the current studies have gone under severe criticism from scholars, economists, sociologists, and political scientists discussing the veritability of the isolated deterrent effect.
Justin Wolfers, an economist at the University of Pennsylvania, wrote in the Stanford Law Review in 2005. “The existing evidence for deterrence,” they concluded, “is surprisingly fragile.”
And with the Supreme Court's new moratorium on lethal injections, these studies play a key role in determining the ethical purpose and place that lethal execution has within our legal system.
What role should it play?