Friday, October 21, 2011

Bad Math

A prosecutor's closing argument on the mathematical possibility of an erroneous eyewitness identification resulted in the reversal of a robbery conviction by the Massachusetts Supreme Judicial Court.

The court evaluated the argument:

The gist of the prosecutor's argument to the jury was that there was a one in forty-nine chance that the victim would have identified as his assailants two persons who knew each other well and therefore a ninety-eight per cent probability that the victim had accurately identified the defendant as one of the assailants, which constituted proof beyond a reasonable doubt. The apparent simplicity of the mathematics belies the complexity of the conclusion regarding the probability of an accurate identification, and conceals the assumptions implicit in the conclusion.

It is true that, if the victim were shown two arrays of six photographs and given a seventh choice of "none of the above," and if the victim closed his eyes and randomly selected one of the seven options in each array, there was a one in forty-nine chance that he would select any combination of two. But if the identification were truly random, it would have no evidentiary consequence. The victim's eyewitness identification has potential evidentiary consequence only to the extent that it is not random, but reflects his recognition of two persons who had robbed him approximately ninety minutes before the identification procedure. For this reason alone, the prosecutor's probability analysis is false and misleading. And without the implicit assumption of random selection, the probability analysis, at a minimum, becomes far more complex.

There are two other fundamental problems with the probability analysis. First, the victim testified that he saw the assailant in the hooded sweatshirt "a lot more," and picked him from the array "[a]lmost right away." Having identified Pacheco from the first array, the probability that the victim would randomly select the photograph of a person Pacheco knew well from the second array depended on how many people in the second array Pacheco knew well. But there was no evidence whether Pacheco knew the other persons depicted in the array, even though the prosecutor obtained an order of immunity and called Pacheco to testify. Nor was there any evidence as to the source of the photographs that comprised the array, apart from Officer Kimball's testimony that he put the victim's physical descriptions of the assailants into "our computer database" and "look[ed] up" people who had been arrested. If the computer database only contained photographs in the possession of the Fall River police department, and if the photographs were selected to reflect persons similar in age to Pacheco, it would not be surprising if Pacheco knew others whose photographs were in the second array apart from the defendant. Therefore, implicit in the prosecutor's argument was the factual representation that the defendant was the only person in the second array whom Pacheco knew, a fact not in evidence.

The court had serious concerns about a wrongful conviction:

 Our conclusion is strengthened by the evidence of the defendant's innocence: Pacheco's testimony that Dias, not the defendant, committed the robbery with him; Dias's testimony that he committed the robbery with Pacheco, and Bennett's testimony that the defendant was baby-sitting her children on the evening of the robbery. While the jury apparently did not credit this evidence, it cannot be ignored in evaluating whether there was a substantial risk of a miscarriage of justice.

The defense had not objected to the argument.

The link timed out. The case is Commonwealth v. Ferreira. (Mike Frisch)

http://lawprofessors.typepad.com/legal_profession/2011/10/bad-math.html

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Comments

Do you have the case name, cite or a link. Clicking on reversal got me nothing.

Posted by: Rick Underwood | Oct 21, 2011 10:47:22 AM

Is this reversal in Ferreira?

Posted by: Rick Underwood | Oct 21, 2011 10:53:25 AM

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