The Devil and Sherlock Holmes by David Grann Page B

determining the cause of a blaze. By the nineties, Hurst had begun devoting significant time to criminal-arson cases, and, as he was exposed to the methods of local and state fire investigators, he was shocked by what he saw.
    Many arson investigators, it turned out, had only a high-school education. In most states, in order to be certified, investigators had to take a forty-hour course on fire investigation, and pass a written exam. Often, the bulk of an investigator’s training came on the job, learning from “old-timers” in the field, who passed down a body of wisdom about the telltale signs of arson, even though a study in 1977 warned that there was nothing in “the scientific literature to substantiate their validity.”
    In 1992, the National Fire Protection Association, which promotes fire prevention and safety, published its first scientifically based guidelines to arson investigation. Still, many arson investigators believed that what they did was more an art than a science—a blend of experience and intuition. In 1997, the International Association of Arson Investigators filed a legal brief arguing that arson sleuths should not be bound by a 1993 Supreme Court decision requiring experts who testified at trials to adhere to the scientific method. What arson sleuths did, the brief claimed, was “less scientific.” By 2000, after the courts had rejected such claims, arson investigators increasingly recognized the scientific method, but there remained great variance in the field, with many practitioners still relying on the unverified techniques that had been used for generations. “People investigated fire largely with a flat-earth approach,” Hurst told me. “It looks like arson—therefore, it’s arson.” He went on, “My view is you have to have a scientific basis. Otherwise, it’s no different than witch-hunting.”
    In 1998, Hurst investigated the case of a woman from North Carolina named Terri Hinson, who was charged with setting a fire that killed her seventeen-month-old son, and faced the death penalty. Hurst ran a series of experiments re-creating the conditions of the fire, which suggested that it had not been arson, as the investigators had claimed; rather, it had started accidentally, from a faulty electrical wire in the attic. Because of this research, Hinson was freed. John Lentini, a fire expert and the author of a leading scientific textbook on arson, describes Hurst as “brilliant.” A Texas prosecutor once told the Chicago Tribune, of Hurst, “If he says it was an arson fire, then it was. If he says it wasn’t, then it wasn’t.”
    Hurst’s patents yielded considerable royalties, and he could afford to work pro bono on an arson case for months, even years. But he received the files on Willingham’s case only a few weeks before Willingham was scheduled to be executed. As Hurst looked through the case records, a statement by Manuel Vasquez, the state deputy fire marshal, jumped out at him. Vasquez had testified that, of the roughly twelve hundred to fifteen hundred fires he had investigated, “most all of them” were arson. This was an oddly high estimate; the Texas State Fire Marshals Office typically found arson in only fifty per cent of its cases.
    Hurst was also struck by Vasquez’s claim that the Willingham blaze had “burned fast and hot” because of a liquid accelerant. The notion that a flammable or combustible liquid caused flames to reach higher temperatures had been repeated in court by arson sleuths for decades. Yet the theory was nonsense: experiments have proved that wood and gasoline-fuelled fires burn at essentially the same temperature.
    Vasquez and Fogg had cited as proof of arson the fact that the front door’s aluminum threshold had melted. “The only thing that can cause that to react is an accelerant,” Vasquez said. Hurst was incredulous. A natural-wood fire can reach temperatures as high as two thousand degrees Fahrenheit—far hotter than the melting