Lyons - population 3,520 - is known as the Peppermint Village, with a bandstand, greenery, and nostalgic brick and clapboard structures straight out of a model railroad set. In his office on William Street, Mitchell fills cavities and the like, but the original CSI, and then 9/11, motivated him to take up forensic dentistry and forensic anthropology. Seven years ago, he started driving twice a month, almost an hour each way, to the medical examiner's office in Brighton.