On this day, May 7, in 1896, Dr. H.H. Holmes, the mass murderer who tortured and killed dozens of guests inside his Chicago hotel, was executed by hanging.

Holmes admitted to 27 murders, but the total count could be more than 100, many during the 1893 World's Fair.

Holmes built a block-long mansion with secret passageways, fake walls and trapdoors. He'd fill guestrooms with lethal gas then take the victims to a basement lab to dissect them. He called his hotel The Castle.

Holmes' killing spree came to an end when detectives investigating an insurance scam found the bodies of two of his victims in Toronto.

Holmes' story was revived in the 2003 book by Erik Larson, "The Devil in the White City." Leonardo DiCaprio bought the rights to make the movie.

-Scott McCabe