I had an idea in the shower a few weeks ago about a design for an effective system of capital punishment. I had been meaning to write it down, when this thread reminded me of it: http://www.thehendonmob.com/forum/viewtopic.php?t=24024&postdays=0&postorder=asc&start=15
I should point out haven't studied this subject in any depth, so it's just a logical framework that meets the popular criticisms I have heard in standard pub-debates - poor deterrence and false positives.
So here's the logical leap, the capital offences are the minor crimes, but they carry a very low chance of the sentence being carried out, in fact to be punished in full you also have to be convicted of a major life-sentence type crime.
Here's how it works; a warning, booking, and then you're on a red card next. Or imagine that every innocent citizen is given an "Avoid Execution Free" card (certainly not "Get Out Of Jail Free", though). For their first crime they are warned, and for their 2nd crime they have to hand back the card. After that, capital crimes are capital.
Again, a first time shoplifter is arrested and punished just as now, with the addition of a full description of the punishment regime for future crimes, if caught shoplifting a 2nd time it's the usual punishment but in addition he now knows that if he is later convicted of murder, rightly or wrongly, he will be executed.
We now have a capital deterrence for minor crime, because if convicted of murder they'll be executed, losing their 40 years' appeal time, even if they didn't do it.
And we have an approximately zero chance of executing an innocent person, because if you had a clean slate (or just one minor offence) at the murder conviction the sentence will be life in prison. If you had already committed two offences it doesn't matter if you actually committed the murder, you are serving the jackpot sentence for shoplifting.
In order for this execution to create a moral dilemma we need to envision three, separate, wrongful convictions. I think that is a low enough probability to go ahead and save all the money we spend giving criminals room and board for their last 50 years.