I first learned of H. H. Holmes when I read Erik Larsen’s fabulous account of the Chicago World’s Fair in The Devil and the White City http://www.amazon.com/Devil-White-City-Madness-Changed/dp/0375725601/ref=sr_1_1?s=books&ie=UTF8&qid=1303743037&sr=1-1
In a nutshell, H. H. Holmes built a “murder castle” a few blocks from the fair. It was billed as a hotel, but what the guests, many of whom were young women, did not know was that many of the rooms were soundproofed and equipped with gas lines that let in…gas, whereby the trapped inhabitant would suffocate. Holmes used a secret chute to drop his victims’s bodies into his basement wherein he had constructed an incinerator room and an acid pit. Furthermore, Holmes would often sell the skeletal remains of his victims to medical schools.
Holmes managed to build the castle without any of his hired construction crews ever knowing the true nature of his architectural schemes. He did this by firing workers and hiring other workers and then firing them in order to ensure that know one really knew what the hell they were building.
There’s a pretty good documentary about Holmes on Netflix Instant Watch titled H.H. Holmes America’s First Serial Killer: http://www.hhholmesthefilm.com/
However, I think Larsen’s book is also worth your time.