Two weeks after Joshua Lipton was charged in a drunken driving crash that seriously injured a woman, the 20-year-old college junior attended a Halloween party dressed as a prisoner. Pictures from the party showed him in a black-and-white striped shirt and an orange jumpsuit labeled “Jail Bird.”

In the age of the Internet, it might not be hard to guess what happened to those pictures: Someone posted them on the social networking site Facebook. And that offered remarkable evidence for Jay Sullivan, the prosecutor handling Lipton’s drunken-driving case.