Could a little-understood mental disorder called Asperger's syndrome clear Billy Cottrell of ecoterrorism charges? Cottrell, 24, is a brilliant but quirky physics grad student at the California Institute of Technology who faces trial in Los Angeles on federal arson counts that may send him to prison for life. Prosecutors charge that he and two unnamed conspirators torched 14 Hummers and a building during an Aug. 22, 2003, spree in which 125 SUVs worth $3.5 million were burned or spray-painted with slogans like SUV = TERRORISM. The vandals claimed responsibility in the name of the Earth Liberation Front, a shadowy group that says it has destroyed property worth more than $100 million nationwide. In a statement, Cottrell, who pleaded not guilty, said he never committed arson, but he hasn't denied being present that night. His lawyers hope to explain the apparent contradiction by showing that Cottrell has Asperger's syndrome, a mild form of autism marked by an impaired ability to comprehend social situations. "The question is: how can somebody so smart be so dumb?" says his attorney Marvin Rudnick. "And Asperger's answers that question."

Certainly, Cottrell's behavior was odd. According to FBI documents, he put the bureau on his trail by writing an arcane equation on one of the SUVs, then bragging about it in an anonymous e-mail traced to a Caltech computer.

Rudnick won't explain how the defense team plans to use the Asperger's defense, but he insists it's legitimate. "This isn't junk science," says Rudnick. "This is a recognized disorder." That's true, but legal experts say that may not be enough. "There are a lot of syndromes people can have that aren't legally significant," points out Loyola Law School's Laurie Levenson. But first the defense team has to get past the government's lawyers, who've sought to bar Asperger's testimony "based on relevance," says prosecutor Beverly Reid O'Connell. The judge is expected to rule before the trial starts on Nov. 9.