The 11th season premiere of "History Detectives," which has been reformatted to focus on one iconic mystery per episode, opens with a look at the April 27, 1865, explosion of the Mississippi steamboat SS Sultana, which was packed with Union soldiers. One of the worst maritime disasters in U.S. history, the official death toll was 1547. The team reviews the original investigative report; and examines theories about the cause, including that it was an act of sabotage by a Confederate agent.

The unsolved case of the Servant Girl Murders in 1884-85 Austin, Texas, is investigated. Over the course of a year, six African-American servants and two white women were brutally murdered. The modus operandi was similar in each instance: the assailant attacked the victim with an ax while she slept in bed; and then he dragged her outside, where he raped and mutilated her.

An investigation into the disappearance of Jimmy Hoffa, the former Teamsters president, who was last seen outside the Machus Red Fox Restaurant in Bloomfield Township, Mich., on July 30, 1975.