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"Nobody thought we had any chance at all going in," says Steve Greenberg, the lead attorney for the defense. But the defense tried an unusual strategy: They argued that Dugan was born with a mental illness—psychopathy—that should be considered a mitigating factor because it impaired his ability to control his behavior. Dugan exhibits the antisocial behavior, inpulsivity, lack of remorse, and other characteristics of psychopathy in spades, says Kent Kiehl, a neuroscientist at the University of New Mexico, Albuquerque, and the Mind Research Network, who served as an expert witness for the defense. Dugan scored 37 out of 40 points on the standard diagnostic checklist for psychopathy, putting him in the 99.5th percentile, Kiehl says.

Kiehl conducts research on psychopathy in New Mexico state prisons in which he and colleagues collect life histories, anatomical brain scans, and fMRI scans of brain activity as inmates perform various tasks, including tests of moral reasoning. Using scanners at Northwestern University, Kiehl ran Dugan through a similar battery of tests. Kiehl testified that Dugan exhibited abnormalities similar to those he and others have reported in other psychopaths. Kiehl says he was careful not to stretch beyond what the data show. He didn't claim, for example, that the brain scans prove that Dugan committed his crimes as a result of a brain abnormality. "It's just one piece of evidence that his brain is different," he says.

Jonathan Brodie, a psychiatrist at New York University testified for the prosecution. "I said the scans are of wonderful technical quality, but so what? They're not relevant here," Brodie says. "Using an fMRI scan done in September of 2009 … to indicate a thought process that was going on in 1983 could hardly be more silly."

After 5 hours of deliberation the jury told the judge on 10 November that they'd come to a decision. But before the sentence could be read, the jury asked for more time and the judge sequestered them overnight. The next day they returned with a death sentence for Dugan. According to media reports and interviews with defense attorneys afterwards, the jury initially planned to sentence Dugan to life in prison, with at least one juror holding out against the death penalty, which requires a unanimous vote. The last minute change is highly irregular, says Greenberg, who is planning an appeal.

Although evidence of anatomical abnormalities in the brain has been introduced previously in the sentencing phase of murder cases, and PET scans have been used to show abnormalities in brain metabolism consistent with mental illness, the Dugan case may be a first for fMRI. "I don't know of any other cases where fMRI was used in that context," says Hank Greely, a professor at Stanford Law School and co-director of the MacArthur Foundation Law and Neuroscience Project. Greely notes that the standards for admitting evidence in sentencing hearings are less stringent than those for evidence used to establish a defendant's innocence or guilt. "The penalty phase of a capital case … is a special situation where the law bends over backwards to allow the convicted man to introduce just about any mitigating evidence."

It's hard to know what effect the fMRI scans in particular had on the jury in the Dugan case, but Greenberg says the fact that they deliberated for a total of more than 10 hours shows that it was influential. "This guy was guilty of raping and killing little girls," Greenberg says. "Without the brain imaging stuff the jury would have been back in an hour."