People in Potoma still leave their back doors unlocked and welcome newcomers with pot pies and lemonade on the porch. In this sleepy riverside community that attracts people of all ages to its clean white-sand beaches, picnic-perfect pocket parks, charming Victorian B & Bs, and golf-cart friendly streets, a busy week for the police department usually involves a few parking tickets and an occasional noise complaint about weekend tourists. So when someone attempts to murder a popular teenage girl in her own home and doesn't leave a trace-or a clue to the murder weapon, it's a mad police...