I think you are barking at a wrong tree. I am not a death penalty supporter. In fact, I know (seriously) all the kosher moves - that punishment does not deter crime, that it is meted out more heavily to unpopular minorities and people who cannot afford competent defence, that it is often a barbaric sacrificial ritual to appease the masses; as well as not so kosher ones - that it is dissolution of traditional social controls rather than poor living conditions that cause criminal behavior, that many crimes are forms of asserting one's respectability in certain subcultures and thus have nothing to do with capitalism.
Moreover, while I am not a death penalty supporter, I do not oppose it too categorically either on the pain of adopting a principle that would compel me to renounce the right to abortion or euthanasia. More generally I think that anything pertaining to social transgressions and sanctions is a grey area with no place for certainty and categorical black-white imagery.
All I am arguing is that: - crime an punishment are prominent features of the mainstream jurisprudence - that despite instances of abuse, the fairness of the justice system is upheld as a matter of principle by the mainstream political forces; - transgressions and sanctions are ubiquituous in every society and thus there is no direct connection between crime and punishment and the main struggle of the marxist left - which is the fair distribution of the surplus rather than the renouncement of every aspect of capitalism and it symbols; - ergo, law enforcement/criminal justice system are quite tangential to the main struggle of the left; they might provide rhetorical ammunition to denounce "the system" and mobilize support behind a cult leader or, conversely, become the focus of bourgeois ideology concerned with formal fairness, but they are pretty inconsequential for the organized struggle of wealth producers to get a fair share of that wealth.
In plain English, I think the Left is wasting a lot of energies by focusing on criminal justice system instead of the organization of production. But that does NOT mean support for the current law enforcement policies either.
I think that the left's position on criminal justice should resemble that of Rosa Luxemburg toward 1st world war - it is a bourgeois struggle, and the working class has no interest in supporting either side in that struggle.
wojtek