Portland lawyer Brandon Mayfield speaks at a press conference May 24, 2004 in Portland, Oregon. Mayfield was exonerated of involvement in terrorist activities connected with the train bombings in Spain. Greg Wahl-Stephens/Getty Images

During a live Web chat in late January, National Security Agency whistle-blower Edward Snowden explained one of the least discussed dangers of bulk collection. By indiscriminately sweeping up the call records and the international communications of Americans, the government has the ability to engage in retroactive investigation, or mining the historical data of targets for any evidence of suspicious, illegal or simply embarrassing activities. It is a disturbing capability that should make even those fully convinced of their own propriety to think twice before uttering out loud, “What do I have to fear if I have nothing to hide?” But there’s another danger that Snowden didn’t mention that’s inherent in the government’s having easy access to the voluminous data we produce every day: It can imply guilt where there is none. When investigators have mountains of data on a particular target, it’s easy to see only the data points that confirm their theories — especially in counterterrorism investigations when the stakes are so high — while ignoring or downplaying the rest. There doesn’t have to be any particular malice on the part of investigators or analysts, although prejudice no doubt comes into play, just circumstantial evidence and the dangerous belief in their intuition. Social scientists refer to this phenomenon as confirmation bias, and when people are confronted with data overload, it’s much easier to weave the data into a narrative that substantiates what they already believe. Criminologist D. Kim Rossmo, a retired detective inspector of the Vancouver Police Department, was so concerned about confirmation bias and the investigative failures it causes that he warned police officers in Police Chief magazine to always be on guard against it. “The components of confirmation bias,” he wrote, “include failure to seek evidence that would disprove the theory, not utilizing such evidence if found, refusing to consider alternative hypotheses and not evaluating evidence diagnosticity.” To get a better sense of the dangers, consider the case of Brandon Mayfield.

Mistaken identity

On March 11, 2004, Al-Qaeda-inspired terrorists coordinated a massive bombing of the Madrid commuter train system during the morning rush hour, killing 193 people and wounding approximately 1,800. Two latent fingerprints recovered during the investigation on a bag of detonators by the Spanish National Police (SNP) were shared with the FBI through Interpol. When the prints were run through the bureau’s database, it returned 20 possible matches for one of the fingerprints, one of whom was Brandon Mayfield. A former U.S. Army platoon leader, Mayfield was now an attorney specializing in child custody, divorce and immigration law in Portland, Ore. His prints were in the FBI system because of Mayfield’s military service as well as an arrest two decades earlier because of a misunderstanding. The charges were later dropped. Despite finding that Mayfield’s print was not an identical match to the print left on the bag of detonators, FBI fingerprint examiners rationalized away the differences, according to a report by the Department of Justice’s Office of the Inspector General (OIG). Under the one discrepancy rule, the FBI lab should have concluded Mayfield did not leave the print found in Madrid — a conclusion the SNP reached and repeatedly communicated to the FBI. The FBI’s Portland field office, however, used that fingerprint match to begin digging into Mayfield’s background. Certain details of the attorney’s life convinced the agents that they had their man. Mayfield had converted to Islam after meeting his wife, an Egyptian. He had represented one of the Portland Seven, a group of men who tried to travel to Afghanistan to fight for al Qaeda and the Taliban against U.S. and coalition forces in a child custody case. He also worshipped at the same mosque as the militants. In the aftermath of 9/11, these innocent associations and relationships, however tangential, were transformed by investigators into evidence that Mayfield wasn’t a civic-minded American, but a bloodthirsty terrorist intent on destroying the West.

Mayfield’s biographical details, particularly his religion and representation of an alleged terrorist, contributed to the FBI lab’s reluctance to re-examine the mistaken identification. According to the OIG, “One of the examiners candidly admitted that if the person identified had been someone without these characteristics, like the Maytag repairman, the laboratory might have revisited the identification with more skepticism and caught the error.” Because the FBI agents had no concrete evidence that Mayfield was linked to the Madrid train bombings, they decided not to apply for a criminal wiretap, which requires probable cause to believe there is criminal activity or intent. Rather, they applied for a Foreign Intelligence Surveillance Act (FISA) warrant, asserting they had probable cause to believe Mayfield was acting on behalf of a foreign terrorist group. This allowed the FBI to circumvent the Fourth Amendment because evidence of criminal activity incidentally discovered in the course of its intelligence activities could be shared with prosecutors and criminal investigators. The secret FISA court approved the request, as it almost always does, and the FBI began its surreptitious and incredibly intrusive blanket surveillance of Mayfield and his family.

Concocted theories

FBI agents broke into Mayfield’s home and law office. They rifled through documents protected by attorney-client privilege, wiretapped his phones, analyzed his financial records and web browsing history, and went through his garbage. They followed him wherever he went. Despite all this, the FBI never found a smoking gun connecting him to Madrid. They did, however, find Internet searches of flights to Spain and learned that he once took flying lessons. To FBI agents already convinced of his guilt, this was all evidence of Mayfield’s terrorist heart. The Web searches, however, were mundane. His daughter had to plan a fictional vacation for a school project. Flight lessons were indicative of nothing more than Mayfield’s interest in flying. While it may seem like there were a freakish number of coincidences here, when the FBI was confronted with evidence that demonstrated Mayfield’s innocence, they twisted it to support their original theory of his guilt. With no evidence that Mayfield had traveled internationally for years — his passport had expired, and the last record of foreign travel was during his military service in 1994 — the FBI simply concocted the theory that he must have traveled overseas as part of this terrorist conspiracy under a false identity.

The bulk collection of Americans’ personal data makes it more likely that false positives — innocent Mayfields coming under government scrutiny — will occur.

Because of mistakes made by the FBI — they left shoe prints in the carpet of the Mayfields’ home and broke in one time when Mayfield’s son was home alone — Mayfield concluded he was under surveillance by federal authorities. Paranoia set in. When driving, he would look to see if someone was following him home or to the office. The FBI took his skittishness as more evidence of his guilt. Believing their cover blown, FBI agents detained Mayfield as a material witness to the Madrid bombing because they feared he was a flight risk. They couldn’t arrest him because their intrusive surveillance still could not find any evidence of any crime. He spent two weeks in jail, petrified that fellow inmates would learn he was somehow involved in the Madrid bombing and hurt him. During the OIG’s review of the handling of the Mayfield case, it found that the FBI’s requests for material witness and criminal search warrants “contained several inaccuracies that reflected a regrettable lack of attention to detail.” The FBI’s belief that it had their man, despite all contrary evidence, was so strong that it provided misleading sworn statements to a judge. The only reason Mayfield is a free man today is that the Spanish police repeatedly told the FBI that the print recovered from the bag of detonators didn’t match Mayfield’s fingerprints. The FBI, however, continued to stand by its lab’s findings until Spanish authorities conclusively matched the print to the real culprit, Algerian national Ouhane Daoud. Only then did Mayfield’s traumatic journey into the stomach of the national security state end.

Cautionary tale