The Brandon Mayfield case is the 2004 wrongful arrest of an Oregon attorney whose fingerprint the FBI incorrectly matched to evidence from the Madrid train bombings. Mayfield spent roughly two weeks in federal custody without being charged with a crime. Spanish police eventually identified the real suspect, the FBI withdrew its identification, and the government paid Mayfield $2 million, issued a formal apology, and changed how its laboratory verifies fingerprint matches.
The Fingerprint Misidentification
On March 11, 2004, ten bombs detonated on four commuter trains in and around Madrid’s Atocha Station, killing 191 people and injuring more than 1,800. Spanish authorities recovered a partial fingerprint on a plastic bag containing detonating devices. That print, designated LFP 17, was shared with the FBI through Interpol.
The FBI ran the print through its Integrated Automated Fingerprint Identification System. Mayfield’s prints were on file because he had served in the U.S. Army from 1985 to 1994. The automated search returned a candidate list, and Mayfield’s name appeared on it.
Three senior FBI fingerprint examiners then independently reviewed the partial print and each concluded it was a “100 percent match” to Mayfield. A fourth examiner, Kenneth Moses, was selected by Mayfield’s own defense attorneys and approved by the court to conduct an independent review. Moses also confirmed the identification, testifying that the latent print belonged to Mayfield’s left index finger.
The failure was human, not mechanical. There is no universal standard for how many matching features are needed to declare a positive fingerprint identification; the call is left to the individual examiner’s training and judgment. Four experienced professionals looked at the same partial print and reached the same wrong conclusion.
Secret Searches Before the Arrest
Before Mayfield knew he was a suspect, the FBI obtained warrants under the Foreign Intelligence Surveillance Act to search his home and law office without telling him. On March 18, 2004, agents entered his residence, photographed his belongings, and copied his computer hard drive. Two days later, they did the same at his law office. Agents also seized documents and electronic media from both locations.
Mayfield, his wife, and his three children had no idea the government had been inside their home. Because the covert searches extended to a lawyer’s office, they reached materials protected by attorney-client privilege.
Arrest as a Material Witness
On May 6, 2004, agents arrested Mayfield under a material witness warrant and booked him into the Multnomah County jail in Portland. The government did not charge him with a crime. The federal material witness statute allows detention of a person whose testimony is considered important to a criminal proceeding; critics have argued the government used it here to hold a suspect while investigators built a case.
The supporting affidavit did not rest on the fingerprint alone. It also cited Mayfield’s conversion to Islam, his marriage to an Egyptian-born woman, and his prior legal representation of a man convicted on terrorism-related charges. Mayfield insisted the print was not his and pointed out that he had not left the United States in more than a decade.
How the Error Was Uncovered
Throughout this period, the Spanish National Police were telling the FBI they disagreed with the identification. As early as mid-April 2004, the Spanish police informed the Bureau that their own comparison of Mayfield’s prints to LFP 17 had come back negative. FBI examiners responded that they were “absolutely confident” in their conclusion.
On May 19, 2004, the Spanish National Police positively identified the latent print as belonging to an Algerian national named Ouhnane Daoud. Faced with a definitive match to another person, the FBI could no longer hold its position. The FBI Laboratory formally withdrew its identification on May 24, the material witness proceeding was dismissed, and the federal judge vacated the warrant. Mayfield walked free.
The $2 Million Settlement and Apology
Mayfield and his family sued the Department of Justice and the FBI, alleging unlawful arrest, false imprisonment, unlawful surveillance, and Fourth Amendment violations. The complaint also brought a Privacy Act claim, alleging the FBI had leaked information about him to national and international media, portraying him as a terrorist before any charges were filed.
In November 2006, the government settled. The terms included $2 million in compensatory damages, a formal written apology to Mayfield and his family, destruction of all documents from the FISA surveillance, and the return of all seized physical materials. The apology acknowledged “the suffering caused by the FBI’s misidentification of Mr. Mayfield’s fingerprint and the resulting investigation.” The settlement preserved one claim for Mayfield to keep pursuing: his constitutional challenge to the Patriot Act provisions that had authorized the surveillance.
The Patriot Act Challenge
Mayfield’s lawyers argued that two FISA provisions, as amended by the Patriot Act, violated the Fourth Amendment. Before the Patriot Act, the government could obtain a FISA surveillance order only if gathering foreign intelligence was the primary purpose of the search. The Patriot Act lowered that bar, requiring only that foreign intelligence gathering be a “significant purpose.” In practice, that let the government use FISA warrants even when its main goal was investigating ordinary criminal activity.
In September 2007, U.S. District Judge Ann Aiken ruled in Mayfield’s favor, declaring that 50 U.S.C. §§ 1804 and 1823, as amended by the Patriot Act, violated the Fourth Amendment. It was the first time a federal court had struck down a Patriot Act provision on constitutional grounds.
The ruling did not survive. In December 2009, the Ninth Circuit Court of Appeals reversed, but not on the merits. It held that Mayfield lacked standing because the settlement had already substantially addressed his injuries, so a declaratory judgment would not require the government to do anything further. The district court’s decision was vacated without the appeals court ever ruling on whether the Patriot Act provisions were constitutional.
Why the Error Happened
The Department of Justice Office of the Inspector General reviewed the case and identified confirmation bias as the primary cause. Once the automated system flagged Mayfield’s print as a candidate and the first examiner declared it a positive match, every subsequent reviewer approached the comparison expecting agreement. Each verification was supposed to be independent, but each examiner knew the previous one had already declared a match.
The reasoning became circular. Because the fingerprint was treated as confirmed, investigators read Mayfield’s background as corroborating evidence of guilt; because his background looked suspicious to them, it reinforced their confidence in the fingerprint. The OIG concluded that Mayfield’s conversion to Islam and his prior representation of a convicted terrorist were not the primary cause of the error but “likely contributed to the examiners’ failure to sufficiently reconsider the identification after legitimate questions about it were raised.”
The OIG also acknowledged a genuinely unusual similarity between the two prints. Remarkable similarity is not identity, and the examiners failed to give adequate weight to the differences, particularly given the substandard quality of the latent print image.
Reforms to FBI Fingerprint Analysis
The case forced concrete changes at the FBI Laboratory. The most significant was a blind verification policy. A second examiner reviewing a fingerprint conclusion now does so without knowing the identity of the first examiner, the conclusion that examiner reached, or any case information that might create expectations. The verifier receives a packet with the prints and nothing else.
The FBI also revised its standard operating procedures to define each phase of the examination process in more detail, with particular attention to documentation when working with partial or low-quality prints. The OIG recommended moving toward more objective criteria for identifications, noting that the existing approach was “wholly subjective.” The Mayfield case has since been cited widely in debates over the reliability of forensic pattern-matching disciplines, standing as evidence that even experienced examiners in a prominent crime lab can reach the wrong conclusion when institutional culture discourages dissent.