A common argument made by the opponents of the death penalty is that murderers don't think about punishment and therefore can't be deterred.  Has anyone asked the murderers themselves?  Yes, actually, someone has.  Professor Robert Blecker of New York Law School has spent thousands of hours in prisons interviewing convicted murderers.  (In contrast to the dubious statements defendants make to their lawyers during legal proceedings, these interviews are conducted in a context where the inmates have nothing to gain by lying.)  Blecker's research and insights are described in his book, Let the Great Axe Fall.

In March 2010, I participated in a mock trial event in London with Professor Blecker, Professor Paul Cassell, and others.  The full video of that event is here.  Those videos are large and take a long time to download.  I have excerpted Professor Blecker's anecdote on deterrence, complete with the reactions of the wigged English lawyers, into a short video, here.