The Myth of Fingerprints

 Posted on October 10,2007 in Uncategorized

In the Brandon Mayfield case, AFIS listed Mr. Mayfield as one of four people in the system whose fingerprints had features in common with the questioned fingerprint from the bombing in Madrid.

An FBI "Supervisory Fingerprint Specialist", Agent Terry Green, concluded that Mr. Mayfield's left index fingerprint matched the questioned fingerprint.

John T. Massey, an "independent fingerprint examiner" (actually a former FBI employee periodically hired by the Bureau to perform fingerprint examinations), verified that Mayfield's left index fingerprint matched the questioned print.

A senior FBI manager, Michael Wieners, reviewed the alleged match and verified that the questioned print matched Mr. Mayfield's.

The FBI issued a formal report matching Mr. Mayfield's print to the questioned print.

The FBI sent Mr. Mayfield's prints to Spain. The Spanish National Police concluded that there was no match between Mr. Mayfield's prints and the questioned print.

The FBI sent agents to Madrid to meet with the SNP. Spanish authorities "refused to validate" the FBI's conclusion.

An FBI investigator, Richard K. Werder, filed an affidavit swearing that Green, Wieners, and Massey considered the questioned print a "100% positive identification" of Mayfield. (Memo to FBI: Fire them. All of them. Fire Terry Green. Fire Michael Wieners. Fire Richard K. Werder. Never use John T. Massey again. Your credibility depends on it. You might even think of outsourcing future fingerprint analysis - to Spain, for example.)So... grand FBI conspiracy, right? Agents jumping to conclusions because they knew that Mr. Mayfield was the only Muslim on the list of 20 possible matches for the questioned print, right?

Maybe, but when Mr. Mayfield was arrested as a material witness, the court appointed an expert witness to compare the questioned print with Mr. Mayfield's known prints. Mr. Mayfield and his lawyers chose Kenneth Moses to do this job. Moses concluded that the questioned print was Mayfield's left index fingerprint. (Memo to the defense bar: Kenneth Moses may not be the best guy to do this work.)

The FBI claims that "fingerprints offer an infallible means of personal identification." Why do we believe that no two fingerprints are alike? No two people have ever been shown to share fingerprints, but there's no reason that two identical fingerprints couldn't exist, and the number of people whose fingerprints have actually been compared is minuscule compared to the billions of people alive today.

Simon Cole says, "The claim that no fingerprint has ever appeared twice was first popularized more than a hundred years ago, and by dint of analogy (with other natural objects like snowflakes), lack of contradiction and relentless repetition, this bit of folk wisdom became deeply enshrined."

The idea that no two fingerprints are alike is nonsense at worst and irrelevant at best. Often fingerprint examiners are comparing sloppy latent prints with tidy known prints; we know that, in this situation, two fingerprints can be alike enough that experts - especially experts with preconceived notions or an axe to grind - cannot distinguish them.