In my opinion, the main contribution a group of rationalists could make to criminal justice reform is to point out that, under certain plausible assumptions about goals, some policies are strictly counterproductive.
For example, most academics who use quantitative studies to investigate the effect of jail sentences find that jail time increases recidivism rates. In other words, putting someone in jail makes them likely to commit more total crimes over the rest of their life as compared to simply being released immediately. This is one decent paper on this topic that isn't behind a paywall; Professor Ian Shapiro at Yale University can refer you to more recent, more damning papers. If you believe this evidence, it follows that pushing long jail sentences to cause specific deterrence is flat-out irrational, and should be discontinued.
Likewise, jail time is highly unlikely to "make victims whole," nor does it seem especially well-suited to this task. I am not aware of any evidence showing that victims claim, in surveys, that having criminals in jail makes them more whole, let alone that said victims enjoy objectively healthier, happier, or more successful lives when perps are in jail. The Athenian system described in one of the other comments here, in which prosecutors (or perhaps even victims) propose a punishment, seems like it would strictly dominate a strategy that basically said "let's put X in a box and force him to do nothing." Making people do nothing, at best, causes nothing to happen. To me, at least, this seems like the sort of insight that is available to rationalists and useful to the outside world even if we can't agree on how to trade off one goal against another.
...For example, most academics who use quantitative studies to investigate the effect of jail sentences find that jail time increases recidivism rates. In other words, putting someone in jail makes them likely to commit more total crimes over the rest of their life as compared to simply being released immediately. This is one decent paper on this topic that isn't behind a paywall; Professor Ian Shapiro at Yale University can refer you to more recent, more damning papers. If you believe this evidence, it follows that pushing long jail sentences to cause speci
The following will explore a couple of areas in which I feel that the criminal justice system of many Western countries might be deficient, from the standpoint of rationality. I am very much interested to know your thoughts on these and other questions of the law, as far as they relate to rational considerations.
Moral Luck
Moral luck refers to the phenomenon in which behaviour by an agent is adjudged differently based on factors outside the agent's control.
Suppose that Alice and Yelena, on opposite ends of town, drive home drunk from the bar, and both dazedly speed through a red light, unaware of their surroundings. Yelena gets through nonetheless, but Alice hits a young pedestrian, killing him instantly. Alice is liable to be tried for manslaughter or some similar charge; Yelena, if she is caught, will only receive the drunk driving charge and lose her license.
Raymond, a day after finding out that his ex is now in a relationship with Pardip, accosts Pardip at his home and attempts to stab him in the chest; Pardip smashes a piece of crockery over Raymond's head, knocking him unconscious. Raymond is convicted of attempted murder, receiving typically 3-5 years chez nous (in Canada). If he had succeeded, he would have received a life sentence, with parole in 10-25 years.
Why should Alice be punished by the law and demonized by the public so much more than Yelena, when their actions were identical, differing only by the sheerest accident? Why should Raymond receive a lighter sentence for being an unsuccessful murderer?
Some prima facie plausible justifications:
Trial by Jury; Trial by Judge
Those of us who like classic films may remember 12 Angry Men (1957) with Henry Fonda. This was a remarkably good film about a jury deliberating on the murder trial of a poor young man from a bad neighbourhood, accused of killing his father. It portrays the indifference (one juror wants to be out in time for the baseball game), prejudice and conformity of many of the jurors, and how this is overcome by one man of integrity who decides to insist on a thorough look through the evidence and testimony.
I do not wish to generalize from fictional examples; however, such factors are manifestly at play in real trials, in which Henry Fonda cannot necessarily be relied upon to save the day.
Komponisto has written on the Knox case, in which an Italian jury came to a very questionable (to put it mildly) conclusion based on the evidence presented to them; other examples will doubtless spring to mind (a famous one in this neck of the woods is the Stephen Truscott case - the evidence against Truscott being entirely circumstantial.
More information on trial by jury and its limitations may be found here. Recently the UK has made some moves to trial by judge for certain cases, specifically fraud cases in which jury tampering is a problem.
The justifications cited for trial by jury typically include the egalitarian nature of the practice, in which it can be guaranteed that those making final legal decisions do not form a special class over and above the ordinary citizens whose lives they effect.
A heartening example of this was mentioned in Thomas Levenson's fascinating book Newton and the Counterfeiter. Being sent to Newgate gaol was, infamously in the 17th and 18th centuries, an effective death sentence in and of itself; moreover, a surprisingly large number of crimes at this time were capital crimes (the counterfeiter whom Newton eventually convicted was hanged). In this climate of harsh punishment, juries typically only returned guilty verdicts either when evidence was extremely convincing or when the crime was especially heinous. Effectively, they counteracted the harshness of the legal system by upping the burden of proof for relatively minor crimes.
So juries sometimes provide a safeguard against abuse of justice by elites. However, is this price for democratizing justice too high, given the ease with which citizens naive about the Dark Arts may be manipulated? (Of course, judges are by no means perfect Bayesians either; however, I would expect them to be significantly less gullible.)
Are there any other systems that might be tried, besides these canonical two? What about the question of representation? Does the adversarial system, in which two sides are represented by advocates charged with defending their interests, conduce well to truth and justice, or is there a better alternative? For any alternatives you might consider: are they naive or savvy about human nature? What is the normative role of punishment, exactly?
How would the justice system look if LessWrong had to rewrite it from scratch?