D worked as a firefighter. twenty-three different fires were intentionally set in the Davy Crockett National Forest, where D was principally assigned to fight fires. D quickly became a suspect in the case. Agent McLaughlin installed a Global Positioning System ('GPS') data logger on D's vehicle. Based on the data from the GPS, Agent McLaughlin placed d's vehicle at the point of origin in three subsequent forest fires. D initially denied setting the fires, he eventually confessed to starting fifteen to twenty of the forest fires. D was charged with three counts of arson. D gave timely notice of his intent to present an insanity defense. D offered two expert witnesses to testify about a neurogenetic defect he has--Klinefelter's Syndrome--and its effect on his ability to appreciate the nature and quality or wrongfulness of his acts. The court held a Daubert hearing. The district court concluded that the experts' testimony should be excluded and, accordingly, refused to give a jury instruction on the insanity defense. D waived his right to a jury trial and was found guilty. D appealed.