BRANDON MAYFIELD….TalkLeft links today to a lengthy New York Times piece about Brandon Mayfield, the Portland lawyer who was arrested because the FBI mistakenly matched his fingerprints with prints found on a blue bag at the scene of the Madrid train bombing last March. The details are pretty chilling:

The F.B.I. officials concluded around March 20 that it was a “100 percent match,” to Mr. Mayfield, according to court records and prosecutors in Portland. They informed their Spanish counterparts on April 2 and included Mr. Mayfield’s prints in a letter to them.

But after conducting their own tests, Spanish law enforcement officials said they reported back to the F.B.I. in an April 13 memo that the match was “conclusively negative.” Yet for for five weeks, F.B.I. officials insisted their analysis was correct.

….Spanish law enforcement officials kept pointing out discrepancies between their analysis and that of the F.B.I., but this did not seem to sink in with the Americans, Mr. Melida [head of the fingerprint unit for the Spanish National Police] said.

….Mr. Melida said an examination of the two prints showed that the arcs on the lower part of the print curved downward in Mr. Mayfield’s print but upward in the print from the bag. In addition, the two prints did not have the same number of concentric rings, or crests, he said. “You’re trying to match a woman’s face to a picture,” he said. But you see that woman has a mole, and the face in the picture doesn’t. Well, maybe it’s covered up with make-up, you say. O.K., but the woman has straight hair and it’s curly in the picture. Maybe the woman in the picture had a permanent?”

….”The Spanish officers told them with all the affection in the world that it wasn’t him,” said a Spanish police official who spoke on condition of anonymity. “We never wanted to simply come out and say the F.B.I. made a mistake. We tried to be diplomatic, not to make them look bad, so we just said the case is still open.”

On May 6 the FBI arrested Mayfield on a material witness warrant and kept him in jail for two weeks.

There are several cautionary tales in this fiasco, but here are the ones that jump out at me:

  • If you already have a suspect in mind and it turns out his fingerprints match those at a crime scene, the odds that the match is just a coincidence are pretty small. You’ve probably got the right guy. Conversely, though, if you don’t have a suspect in mind and you just go searching through your database for a match, the odds of making a mistake are pretty high.

    Think of it this way. Suppose you’re at the library looking for a book and you’re pretty sure you’ve found the right one. You know that it starts with the sentence “I love summer,” so you open up the book and, sure enough, that’s the opening phrase. Bingo. After all, even if there are several books that start with that sentence, what are the odds that the book you chose would just happen to start that way unless it was the right one?

    Now turn it around. Suppose you don’t have a particular book picked out. Instead you go to the library database and just search for all books that begin with “I love summer.” And it turns out the library has one. The problem is that if, say, there are five books that start that way, there’s only a 20% chance that your library has the correct one. This is pretty much what happened to the FBI in this case.

  • It’s awfully easy to convince yourself that a theory is correct even if the evidence isn’t very good. Mayfield was a Muslim, he had represented a terrorism defendant in a custody case, etc. Hey, what are the odds? The problem is that these theories can be awfully seductive even when they have lots of holes, as this one did.

  • What if the Spanish hadn’t been involved? If it had been up to the FBI, they would have convinced themselves that Mayfield was their man, shipped him off to Gitmo for “interrogation,” and the real bombers might have gotten away. It wouldn’t be the first time.

  • I don’t like material witness warrants. It’s not a central part of this case, but the fact is that Mayfield was arrested as a material witness, which allows authorities to keep someone locked up indefinitely without charges. This has been abused before and it’s going to be abused again. It’s wrong.

Anyway, keep all this in mind the next time you shake your head over the fact that OJ was acquitted. After all, what happened to Mayfield has probably never happened to you or one of your friends before, has it? But if you had been on the receiving end of stuff like this before, where flimsy evidence was built into a capital case based on little more than simply belonging to the wrong ethnic group, you might have been suspicious of the evidence too.

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