One of the questions surrounding the sex-abuse case against Jerry Sandusky is why a former district attorney chose not to prosecute the then-Penn State assistant coach in 1998 after reports surfaced that he had inappropriate interactions with a boy. The answer is unknowable because of an unsolved mystery: What happened to Ray Gricar, the Centre County, Pa., district attorney? Gricar went missing in April 2005. The murky circumstances surrounding his disappearance — an abandoned car, a laptop recovered months later in a river without a hard drive, his body was never found — have spawned Web sites, television programs and...