Professor Jarvis asks if Lt. Roman thinks he's "some kind of Crippen or Landru." Crippen refers to Hawley Harvey Crippen. His wife disappeared on January 31, 1910, and he was eventually convicted of her murder when her partial remains were found under the brick floor of his basement. He was hanged in London on November 23, 1910. Landru refers to Henri Désiré Landru. He was a serial killer convicted of the assassination of 10 women and one man (though his true victim total was almost certainly higher) between January 1915 and January 1919. He was executed by guillotine in Versailles, France on February 25, 1922.