On a hot, humid Sunday in July 1978 the body of 18-year-old Mary Ellen Tanner was found in a grassy field in Lyman, Maine. A pilot leaving Gracie Evans Field spotted her partially clothed body. The Kennebunk High School senior had been beaten to death with a blunt object and was pregnant; the medical examiner could not determine whether sexual assault had occurred. Investigators believe she was killed elsewhere and her body dumped in a field locals know but outsiders would not easily find.

Two nights earlier, on the evening of Friday, July 7, Mary had been socializing: she attended a festival parade, went to a party in woods off Route 9 in Kennebunk, and later went to Kennebunk Beach. Friends dropped her at the intersection of Routes 9 and 35 around 11:30 p.m.; she said she would hitchhike the last mile to her home. She was last seen on the Mousam River Bridge trying to get a ride; friends who turned back to check on her found she was gone.

The investigation has stretched decades with numerous interviews and several persons questioned, but no arrest has ever been announced and no one has been publicly named as a suspect.