Wednesday, November 21, 2007

When Guilt or Innocence Hangs (Largely) on a (Microscopic) Speck

Some years ago - in 1999 -- Jill Dando, a well-known BBC TV reporter (or "presenter"), was shot to death. In 2001 a man called Barry George was tried and convicted for her murder. A key piece of evidence -- apparently the key piece of evidence -- against George was a "microscopic particle of gun shot residue found in the pocket of a jacket owned by George." Wikipedia Article. But the UK Court of Appeal has just concluded that George's conviction was "unsafe" and it allowed George's appeal (i.e., it vacated his conviction). (But George was not released from custody.)
An article in the Guardian in the summer of 2002 asserted, "The evidence against George - resting primarily on an invisible particle of explosives residue found on the lining of his coat - was remarkably thin. He lived in a cluttered and uncleaned flat." Bob Woffenden, Shadow of Doubt?, Guardian (July 6, 2002)
I have not studied this well-known case, and I have not read the Nov. 15 opinion of the Court of Appeal. But one media account implies that it is possible the Court of Appeal allowed George's appeal (on Nov. 15, 2007) because the Court concluded that there was a real possibility that the police who searched George's apartment inadvertently deposited the microscopic particle on George's clothing. Other sources hint at a slightly different but similar ground for the overturning of George's conviction -- that the argument tying the speck or particle to the gun that was used to shoot Jill Dando was weak and perhaps that the Court of Appeal concluded that it was equally probable that the speck found in the pocket of George's jacket came from a different source, from a source other than the murder weapon. See, e.g., the Wikipedia article cited above. Cf. a BBC news report discussing the argument before the Court of Appeal prior to the ruling by the Court of Appeal:
Dr Ian Evett, an FSS employee since 1966, said his position was one of "vague unease", Mr Clegg [defense counsel] said.

He [Evett?] said an FSS report found "it would be just as likely that a single particle of discharge residue would have been recovered from his pocket whether or not he was the person who shot Miss Dando nearly a year previously".

Needless to say, I need to read the Nov. 15 opinion of the Court of Appeal.

One odd thing about this case is that a well-known "crime science" institute was established in Jill Dando's memory. See UCL Jill Dando Institute of Crime Science

Scientific evidence can be powerful. But sometimes scientific evidence makes a great deal out of physically trifling trifles of evidence. Is the object lesson of the George case this: when scientific inferences rest on physically small trifles (a hair, a speck of dust, etc.) very careful attention must be paid to how the evidentiary trifle might have gotten to where it was found? [For example, was the trifle wafted there by the wind? Was it deposited there by a police officer? Did the cleaning lady {or gentleman} leave it there? Etc.] Or does this case merely teach that the science used to draw inferences from the trifle in question went awry (perhaps due to mistakes by the testifying expert or, alternatively, perhaps because of defective scientific theory)? I shall have to read the opinion. Or, dear Reader, perhaps you will do this for me?

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