Can a fingerprint match be wrong? What happened to Brandon Mayfield?
In 2004 the FBI called a fingerprint a “100 percent match” and a lawyer was held for two weeks over a faulty match.
Yes. In 2004, Brandon Mayfield, an American lawyer, was incorrectly detained in connection with the Madrid train bombings on the basis of a faulty fingerprint match. The FBI arrested him on 6 May 2004 as a and held him for two weeks, then released him with a public apology after Spanish authorities identified another suspect.
The story began with fingerprints on a bag containing detonating devices, found by Spanish authorities and shared with the FBI through . A search of the FBI database returned twenty possible matches. One of them was Mayfield, whose prints were on file from his military service. On 20 March 2004 the FBI concluded that the fingerprints were a "100 percent match".
The Spanish authorities did not agree. In an April memo they contested the match. On 19 May they announced that the prints belonged to an Algerian national, Ouhnane Daoud, and Mayfield was released the next day. A United States Department of Justice review later acknowledged serious errors in the FBI investigation, and lawsuits ended in a 2 million dollar .
20 Mar
The FBI concludes the print is a “100 percent match”
13 Apr
Spanish authorities contest the match in a memo
6 May
Mayfield is arrested as a
19 May
Spain announces the prints belong to Ouhnane Daoud
20 May
Mayfield is released
Does that mean fingerprints are unreliable? Not exactly. Matching two fingerprints is among the most widely used and most reliable techniques. But the case showed that a "match" is a judgment made by people: here a print picked from twenty possible matches was called certain, and it was wrong.
Quiz me
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Recap
A fingerprint “match” is a human judgment, and even one called “100 percent” can be wrong.
💡 A trick to remember it · One print, twenty look-alikes: the examiner picks one, so the pick needs a second pair of eyes.
Surprising fact · The FBI called the print a '100 percent match', yet Spanish authorities contested it in April and found the real owner in May.
Connects to
- 🦷 Why were bite-mark and hair comparisons discredited as forensic evidence?
- ⚖️ Why is a suspect treated as innocent until proven guilty?
- 👆 Did a novelist use fingerprints as evidence before the police did?
- 👁️ Can thousands of eyewitnesses get it wrong?
- 🔍 Why do we notice only the evidence that proves us right?
- Dna profiling
Sources (2)
No source, no claim. Every fact in this lesson (14 claims) cites at least one of these.