My apologies to readers who may find the following a bit scrappy in style - it is Sunday and I ought to be doing other things in my real life!
Scotland, where the murder rate is double that south of the border, is now considering allowing “double jeopardy”; that is, trying someone more than once for the same offence (this has been possible in England since 2005). Libertarians will worry that the State can persecute individuals using judicial process; even that possibility is something of an extra burden on the citizen.
Penalties for the most serious crime, murder, are not so severe as they once were. There is no death penalty, and life imprisonment rarely turns out to be that: the average time served for mandatory lifers in the UK is 14 years. (Other, non-mandatory life sentences end up as 9 years served, on average.)
Perhaps one could work out the change in penalty as some kind of life-related formula. Let's assume for the sake of argument that life in prison is the same as no life at all. In that case, the death penalty is the loss of 100% of the rest of one's life, irrespective of the time between conviction and execution.
By contrast, how much of the criminal's life does life imprisonment take away? It depends on how old he is when the crime is committed, and how long he might be expected to live afterwards. I can't easily find statistics on the average age of murderers in the UK, but in the US it appears to be around 27. In the UK, life expectancy at birth varies for males according to social class, from 80 to 73 years (further complicated, I should expect, by variations in infant and juvenile mortality rates). Thus the penalty of life imprisonment represents 14/(73 - 27)% = 30% of remaining life.
I've read that before capital punishment was abolished, British juries were more reluctant to convict in cases where the death sentence might be imposed, but I can only guess at how far this might alter the probability of a "guilty" verdict. Shall we say, a difference of 20%? That would mean a penalty factor of (100*0.8)=80% for the death penalty, versus 30% for "life".
The discrepancy may well be less than this, since for many convicts, prison is safer and healthier than the life they face outside. The retired prison doctor "Theodore Dalrymple" has often noted how his patients throve "inside", where largely they were off illegal drugs and were reasonably well-fed. If after serving his time the ex-convict lives a shorter (nastier, more brutish) life, then his prison sentence has consumed a greater proportion of his post-conviction existence.
Wrongful conviction is always a concern. In Parliament in 2006, Mr O'Hara asked "how many miscarriages of justice there have been in capital cases which have resulted in a payment of compensation in the last 30 years", to which the answer was, that there were only four cases. Perhaps it's because forensic science has advanced very considerably since 1964, when the last execution was carried out in England. But the American experience suggests other factors masking miscarriages of justice, including: "Lawyers in many capital cases are lousier than the norm." There's no making up for a mistake, in the case of capital punishment (unless we return to the ancient principle of "weregeld").
What about deterrence? From the foregoing, "life" seems to be perhaps half as onerous as the death sentence. Yet US criminologists appear to agree that the death penalty does not have a significant deterrent effect. Could we argue that in many murder cases, the circumstances of the crime are such the perpetrator simply doesn't consider the potential consequences for himself? Would the same number of such crimes be committed, even if there were no legal penalty at all?
One might argue that deterrence is not the main point, and the penalty, whatever it may be, is simply a punishment that fits the seriousness of the crime. In which case, why is the crime treated so much less seriously than before?
On the other hand, maybe deterrence is an argument, after all. The journalist Peter Hitchens has argued that the murder rate in Britain would be far higher (I think he said, by a factor of about 10), were it not for huge improvements in medical procedures over the last 40 years, that now save the lives of many victims of violent assault. If that is so, then there may well be a correlation between severity of punishment and the crime rate, after all.
Perhaps greater certainty of conviction is the greatest deterrence; but that can't be easily achieved. If re-trial significantly increases the probability of successful and just conviction, it might go some way towards evening-up the odds in terms of deterrence. But I doubt that it will greatly improve conviction rates overall, not least because there will be opportunities for the defence to claim that the outcome has been prejudiced in some way by matters relating to the previous trial and the associated publicity. And I would think there would not be many re-trials approved by the Crown Prosecution Service (or its Scottish equivalent), since they will have to consider the chances of "a result" second time round, and also bear in mind the issue of the presumed-innocent citizen's right not to have his life consumed by legal pestering, for which monetary compensation may never be sufficient.
So I think it's always going to be extremely important to "get it right first time," and I don't think a second pop at the target is going to make enough difference to justify the inconvenience to the accused in cases that don't succeed.
As to sentencing, an incorrect conviction is always wrong, but a death sentence for the innocent is absolutely wrong. Yet for the guilty, the penalty for murder is far less heavy than it used to be, and that, too, seems unjust and quite possibly it has also been one of the reasons for an increase in potentially lethal assaults.
So to me, it would be better to increase time actually served in jail, in cases where the judge determines that consideration of consequences was, or would likely, or (after making allowance for emotion) ought to have been in the criminal's mind at the time of committing the act. (a) I think it would increase the deterrent effect, and (b) opinion may differ, but I think it would be deserved, at least in "serious" cases.
There should also be the swiftest and fairest treatment of appeals, so that where there has been a miscarriage of justice, the innocent should be released as quickly as possible, and compensated handsomely. The State itself needs a deterrent.