Unsolved Mysteries returns with its first-ever feature length documentary. After forty-six years, one of the greatest mysteries in American true crime may finally be solved. In December of 1982, a man is found dead from cyanide poisoning in a Catholic church in Boise, Idaho. He carries no identification and is buried in an unmarked grave. Decades later, Detective Tim Cooper reopens the case and deciphers a trail of clues that not only identifies the mysterious stranger, but uncovers evidence to prove the man may be one of the most notorious and sought-after mass murderers in our nation’s history… the Tylenol Killer.