72 Hours: True Crime

Stuck at home and bored, a retiree takes a job at a 24-hour convenience store. On her third night at work a customer finds her on the floor behind the register, face down in a pool of blood. Detectives determine that her last customer was also her killer. Only two witnesses saw that customer. And in a town where everyone knows everyone else - he was a stranger. Find the stranger, find the killer. But how do you find a man who's defining characteristic is that no one knows who he is?