I Was There - Season 1 Episode 6 -

Theo Wilson travels back in time to 1893 Chicago, finding himself in the lair of America's first famous serial killer, H.H. Holmes. But how did Holmes become such a prolific murderer? Theo follows Holmes dark road from conman, to the owner of a fiendishly engineered "murder castle," where he hunts his victims in the convenient shadow of the World's Columbian Exposition.