Fingerprint evidence has put innocent people in prison and derailed lives even when multiple trained examiners agreed on the match. The cases where fingerprints were wrong include Brandon Mayfield, wrongly tied to the 2004 Madrid train bombings; Shirley McKie, a Scottish police officer prosecuted for perjury over a misidentified print; Stephan Cowans, who served nearly six years in Massachusetts before DNA cleared him; and Richard Jackson, convicted of murder in Pennsylvania on two bloody prints that turned out not to be his. Each one shows that fingerprint analysis, treated in court as near-certain, depends on human judgment that can fail.
Brandon Mayfield and the Madrid Train Bombings
In March 2004, bombings on commuter trains in Madrid killed 193 people. Spanish police recovered a latent fingerprint on a bag of detonators and shared it through Interpol. The FBI ran the print through its Integrated Automated Fingerprint Identification System, and a senior examiner identified it as belonging to Brandon Mayfield, an American attorney in Portland, Oregon, who had never traveled to Spain.
Two additional FBI examiners verified the identification. An outside court-appointed expert also concurred. On May 6, 2004, the FBI arrested Mayfield as a material witness. He was held at a county detention center in Portland for about two weeks before a judge moved him to home detention on May 20.1Office of the Inspector General. A Review of the FBI’s Handling of the Brandon Mayfield Case
Spanish authorities disputed the match throughout and eventually identified an Algerian national, Ouhnane Daoud, as the actual source of the print. On May 24, the FBI Laboratory withdrew its identification, and the government dismissed the case. The Department of Justice issued a formal apology, stating it “regrets that it mistakenly linked Mr. Mayfield to this attack,” and later settled a lawsuit with him for $2 million.
The FBI’s Office of Inspector General later identified several causes. The initial examiner had failed to complete a thorough analysis of the latent print before searching the database, then disregarded important differences between the crime scene print and Mayfield’s known prints. Overconfidence in the database and the pressure of a high-profile terrorism case compounded the problem. Most damaging, the verification step was “tainted” because the reviewing examiners already knew the first examiner’s conclusion, turning what should have been an independent check into rubber-stamping. The FBI Laboratory attributed the mistake to “practitioner error” rather than a failure of the science itself.1Office of the Inspector General. A Review of the FBI’s Handling of the Brandon Mayfield Case
Shirley McKie and the Scottish Perjury Case
In January 1997, detectives investigating the murder of Marion Ross in Kilmarnock, Scotland, found a fingerprint inside the victim’s house. Examiners at the Scottish Criminal Record Office identified it as belonging to Shirley McKie, a police officer who had been at the crime scene in an official capacity. McKie denied ever entering the house, and no other evidence placed her inside.
Rather than re-examine the print, authorities charged McKie with perjury in March 1998 for denying under oath that she had been in the house. She was acquitted in May 1999 after independent experts testified the print was not hers. A subsequent inquiry by HM Chief Inspector of Constabulary backed McKie and recommended overhauling procedures at the Scottish Criminal Record Office.2BBC News. Inquiry on Shirley McKie Case Blames Human Error
A later public inquiry, led by Sir Anthony Campbell, concluded there was “no evidence” that McKie had entered the victim’s house and that the fingerprint had been “misidentified by SCRO fingerprint examiners due to human error.” The inquiry found “nothing sinister” behind the mistake but made clear that institutional reluctance to admit error had prolonged her ordeal.2BBC News. Inquiry on Shirley McKie Case Blames Human Error
Stephan Cowans and the Boston Shooting
In May 1997, a Boston police officer was shot during a pursuit. The suspect fled through a residential neighborhood, entered a home, and drank from a glass of water before leaving. Investigators recovered a latent fingerprint from the glass, and two Boston Police Department fingerprint analysts identified it as belonging to Stephan Cowans. On June 30, 1998, a jury convicted Cowans of armed assault with intent to murder, home invasion, and other charges. He was sentenced to 35 to 50 years in prison.3The National Registry of Exonerations. Stephan Cowans
Cowans maintained his innocence and eventually connected with the New England Innocence Project. Attorney Robert Feldman secured a court order for DNA testing of the glass, a baseball cap, and a sweatshirt collected from the crime scene. In January 2004, testing by Orchid Cellmark established that DNA on all three items came from one person, and that person was not Cowans. Judge Peter Lauriat granted a new trial on January 21, 2004, and the charges were dismissed on February 2. Cowans had spent nearly six years in prison.
The fallout was significant. The two fingerprint analysts were placed on administrative leave. The department’s entire Latent Fingerprint Unit was temporarily shut down. The Massachusetts Attorney General launched a grand jury investigation but ultimately brought no criminal charges against the examiners.3The National Registry of Exonerations. Stephan Cowans
Richard Jackson and the Bloody Fingerprints
In 1997, Richard Jackson was charged with murder in Delaware County, Pennsylvania. The only physical evidence linking him to the crime was two bloody fingerprints found on a fan near the victim’s body. Three prosecution experts identified the prints as Jackson’s and testified accordingly at trial.
Jackson’s defense presented two experienced examiners who disagreed. Vernon McCloud, who had spent 40 years as a fingerprint examiner for several federal agencies, and George Wynn, a former FBI fingerprint examiner, both testified the bloody prints were not Jackson’s. The jury convicted him anyway.4The National Registry of Exonerations. Richard Jackson
After the conviction, the International Association for Identification investigated one of the prosecution’s experts, Jon Creighton, and concluded he was wrong. Creighton admitted the mistake, and the IAI decertified him as an examiner. Another expert retained by the prosecution later examined the evidence and also concluded the prints were not Jackson’s. The prints were then sent to the FBI, which confirmed they did not belong to Jackson. On December 23, 1999, the judge vacated the conviction. The district attorney called the prints the “keystone of the prosecution’s case” and acknowledged that without them, “there’s no credible basis to accuse him.”4The National Registry of Exonerations. Richard Jackson
Five qualified examiners looked at the same prints and reached opposite conclusions. That kind of disagreement among trained professionals is difficult to square with the idea that fingerprint analysis is objective.
Why These Misidentifications Happen
Fingerprint comparison has no objective numerical threshold for declaring a match. Unlike DNA analysis, where a lab can calculate the probability of a coincidental match, fingerprint examiners rely on visual pattern recognition and experience. Crime scene prints are often smudged, partial, or distorted by the surface they were left on, and the examiner makes a judgment call. Training, fatigue, expectation, and the pressure of a high-profile case all shape that call.
The fingerprint community claimed a zero error rate for decades. Controlled testing has proven otherwise. The FBI-sponsored “Black Box Study” tested 169 latent print examiners on known-answer comparisons and found a false positive rate of 0.1% (about 1 wrong match in every 1,000 comparisons) and a false negative rate of 7.5%.5International Association for Identification. Accuracy and Reliability of Forensic Latent Fingerprint Decisions A 2025 study evaluating examiners on comparisons from the FBI’s Next Generation Identification system found a 0.2% false positive rate and a 4.2% false negative rate, and noted that one participant made the majority of the false identifications.6ScienceDirect. Accuracy and Reproducibility of Latent Print Decisions on Comparisons From Searches of an Automated Fingerprint Identification System Individual examiner skill matters a great deal.
Two major government reviews reached similar conclusions about the underlying method. The 2009 National Academy of Sciences report found that fingerprint comparison relies on “subjective judgments by the examiner” and that “claims of absolute, certain confidence in identification are unjustified.”7Office of Justice Programs. Strengthening Forensic Science in the United States: A Path Forward The 2016 report from the President’s Council of Advisors on Science and Technology called latent fingerprint analysis a “foundationally valid subjective methodology” but warned that the false positive rate “is substantial and is likely to be higher than expected by many jurors,” citing properly designed studies with rates ranging from 1 in 306 to 1 in 18.8Executive Office of the President. Forensic Science in Criminal Courts: Ensuring Scientific Validity of Feature-Comparison Methods
What Has Changed Since These Cases
The most important reform is blind verification, in which a second examiner reviews the work without knowing the first examiner’s conclusion or the case context. NIST defines it as verification where “the subsequent examiner has no knowledge of the original examiner’s decisions, conclusions or observed data used to support the conclusion” and recommends it especially when an identification results from an automated database search.9National Institute of Standards and Technology. Best Practice Recommendations for the Verification Component in Friction Ridge Examination
That reform speaks directly to what went wrong in the Mayfield case, where multiple examiners confirmed a wrong answer because they already expected it to be right. Other changes include enhanced certification requirements, standardized documentation of the features an examiner relied on, and blind proficiency testing in some federal labs, where examiners don’t know whether a case is real or a test. Adoption varies widely across the thousands of state and local forensic labs in the United States, so the safeguards a defendant benefits from can depend on which agency processed the print.