Brandon Mayfield was a US Army veteran and an attorney in Portland, OR. After the 2004 Madrid train bombing, his fingerprint was partially matched to one belonging to one of the suspected bombers, but the match was a poor one. But by this point, the FBI was already convinced they had their man, so they rationalized away the non-matching elements of the print, and set in motion a train of events that led to Mayfield being jailed without charge; his home and office burgled by the FBI; his client-attorney privilege violated; his life upended.
At every turn, the FBI treated evidence that contradicted their theory as evidence that confirmed it. Mayfield's passport had expired and he couldn't possibly have been in Madrid? Proof that he was a terrorist: he must be using his connections with Al Qaeda to get false papers so that his own passport isn't recorded as crossing any borders. Mayfield starts to freak out once he realizes he's under surveillance? Aha! Only the guilty worry about having their homes burgled by G-men!
The FBI was so sure of their theory that they lied to a judge during their campaign against him. His story is the perfect embodiment of "confirmation bias" -- the tendency of human beings to give undue weight to evidence that confirms their existing belief and to discount evidence that rebuts it. Confirmation bias is one of the underappreciated problems of mass surveillance: gather enough facts about anyone's life and you can find facts that confirm whatever theory you have about them.
Or, as Cardinal De Richelieu said: "If you give me six lines written by the hand of the most honest of men, I will find something in them which will hang him." This line is the epitaph in my story Scroogled (here's Wil Wheaton's reading of it), about the risks of automated, unaccountable attributions of guilt based on algorithms that are not subject to scrutiny. But as bad as the automated attribution as guilt can be, it's nothing compared to the directed attribution of guilt from cops who are absolutely sure that they have their man.
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.
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. T
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