Kramer on the "Purgative" Justification for Capital Punishment

Distinguished legal philosopher (and legal positivist) Matthew Kramer is publishing a fascinating-looking book early next year, The Ethics of Capital Punishment: A Philosophical Investigation of Evil and Its Consequences (OUP 2012), in which he offers a critique of current justifications and objections as well as, most intriguingly, a qualified defense of the death penalty for what I believe are particularly atrocious killings.  I have not yet seen the book, so if others with knowledge of it can chime in, I would be grateful.  He calls his partial defense the "purgative" justification.  In this blog post from a few years ago, he describes the defense as Biblically grounded (though he emphasizes that he is "robustly atheistic").  The post is a few years old and it is therefore highly likely that the arguments in the book are changed.  But for interest's sake, here's a bit from that post which may give a rough sense of his "purgative" justification.

Notwithstanding my doubts about the foregoing justifications for capital punishment, I firmly support such punishment in cases of particularly heinous murders. My support is grounded on an alternative rationale, a rationale found prominently in the Bible. (Though I am robustly atheistic, I have long taken the view that one can profit from a good knowledge of the Bible.) We are repeatedly told in the Torah that murderers - and certain other miscreants - should be put to death so that the community can be purged of their contaminating presence. Stripped of its religious trappings, and narrowed to encompass only murders that are especially vile, this purgative rationale for the death penalty is the basis for my stance in favour of capital punishment. A community sullies itself by keeping alive certain people who have acted in such a repugnantly depraved and murderous fashion as to degrade the human species through their membership in it. By sustaining rather than ending the existence of those people, a community retains its association with them - even if they are securely locked away. The only way in which the community and the human species can be purged of the debasing evil of those people is to be purged of those people themselves. That purging never requires torture or displays of heads on pikes; instead, it requires nothing more and nothing less than executions.

This to me all sounds strongly reminiscent of some of the claims made by James Fitzjames Stephen about the social and cultural virtues of expressive punishment; it is one more marker of Stephen's surprisingly contemporary applications.  Kramer acknowledges that his justification sounds in the "denunciatory rationale" (I do not think this adequately captures Stephen's view, but that's another story), though he claims it is different in important ways.  I am looking forward to reading the book to see how he can place the limits on the purging rationale that are reflected in the final part of the indented paragraph above.