David Bain’s guilt isn’t important

Is David Bain guilty of murder? No. That’s what a jury of our peers said on far better information than we now have. Did he kill people? Possibly. Does it matter? No.

Our justice system is designed to acquit people when we cannot be sure of their guilt. In its design there is an implicit judgment that errors of wrongful conviction are worse than errors of incorrect acquittal. Let’s think about that judgment. If you acquit someone who committed an offence then the cost to society is only the cost of their recidivism. Given uncertainty about their guilt, the cost is P(guilty) x P(reoffend) x (damage from reoffending). If you wrongfully convicted someone then the cost is P(not guilty) x (damage from imprisonment).

Suppose P(guilt) > P(not guilty) by a little, so the person is not convicted but we think they probably did it. Given that P(reoffend) is probably ~30%, that means that the damage from re-offending would have to be a lot higher than the damage from imprisonment to make it right to imprison the person. Most murderers do not reoffend by committing another homicide so we can class that outcome as highly unlikely. Given the cost to a person of imprisonment it does not seem unreasonable to make the value judgment that we have implicitly made in the design of our justice system.

On the basis of this approach, the question of whether Bain killed his family is only a curiousity. It has little bearing on whether he should be in jail, since any normal person’s answer to that question is based on a ‘balance of probabilities’ approach. It is commendable that the jury took their responsibilities seriously and did not fall into the trap of going with their gut.

  • goonix

    In this instance P(reoffend) is zero – he has no family left to murder. 😛

  • ben

    Rauparaha, your post was in danger of being half-decent until you wrote:

    It has little bearing on whether he should be in jail, since any normal person’s answer to that question is based on a ‘balance of probabilities’ approach. It is commendable that the jury took their responsibilities seriously and did not fall into the trap of going with their gut.

    Oh good. The Gross Generalisation followed by the Presumption You Couldn’t Possibly Know Is True.

    I thought this blog was about economics. It has become an outlet on Rauparaha’s views on what normal people think. I read your blog for insight, not this. Where is Nolan?

  • Ouch!

  • DT

    What a killer line!
    I wonder whether being there, seeing the accused in the dock in this particular case, it would be more conducive to going with ones gut than for an avid news follower outside the courtroom, who may be more dispassionate.

  • @ben
    Please try to be civil.

    @DT
    Given that what an avid news follower sees is an editorialised narrative rather than the actual trial as presented by the two sides, I don’t think objectivity is enough to reach a conclusion.

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  • John

    Nothing about DB but what about these luxury cars going for bargain prices?

  • steve

    one thing you have missed is the moral hazard from finding the accused not guilty. If it appears easy enough to create reasonable doubt, then there is the additional cost to society of increased crime. Although Bain’s had 13 years of jail already this is prob enough of a deterent (not necessarily overall but lets assume), but this case is precedent for future murder trials whereby they just have to make it possible that it was a murder suicide and get away with it. the additional cost of increased murders must be included in the CBA of finding not guilty, and the additional benefit of decreased murders must be included in the CBA of finding guilty.

    Prob more important for crimes that aren’t crimes of passion like murder, (I assume the deterent of getting caught is relatively low for murder b/c it is not considered at the time of the crime), but crimes such as fraud (where the cost of getting caught is prob considered over a longer period). None the less the moral hazard costs and benefits should be included.

  • @steve
    Good point, Steve, that should definitely be in there. Although, as you point out, it makes more of a difference for premeditated offences since there isn’t much of a deterrent effect for crimes of passion.

  • Dick

    June 11, 2009 -Startling new evidence is revealed that was ruled to be to prejudical and was admissable. The evidence revealed suggests Daivd had been intimidating the family with the rifle used in the killing’s and that he had bosted about getting away with sexual assualt by using his paper run as an alibi. Also the entire 111 call is realeased and digitally enhanced with David thought to have said “I shot the Prick”.

    In 2007 the Privy council ruled that a miscarriage of justice had taken place on the grounds the Jury had not heard all the evidence and were entitled to do so.
    They ordered a retrial and subseqently again the Jury did not get hear all the evidece, which would suggest again there has been a miscarriage of justice.

    What does this now mean ??? Is it time for a retrail.

  • Dick

    Sorry I meant to say he had bosted he could get away with sexual assualt.

  • Deanna

    Perhaps one day members of your family and possibly yourself could be murdered rauparaha – to quote yourself – will it matter? no – depending on the calibre of the jury you and your family would have a 50 percent chance of getting justice.

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