H.H. Holmes, born Herman Webster Mudgett and known for much of his adult life as Dr. Henry Howard Holmes, is credited as America's first known serial killer. While there is no question that H.H. Holmes was a truly evil and disturbed individual, there are many questions surrounding the extent of his crimes.

Suffering through a troubled youth, many say that Holmes trapped and performed surgical experiments on animals from a young age, and some even say he murdered his childhood best friend. Holmes attended the University of Michigan for medical school, where it is rumored that he stole and disfigured cadavers, claiming the people died in accidents to commit insurance fraud.

Holmes is most infamously known for killing more than 200 people during the 1893 Chicago World's Fair in his "murder castle", although that number may be a bit exaggerated. Holmes was only officially charged with the murder of 9 people, and while he did confess to the murder of 27, many of the people he claimed to have killed were still alive when he made his "confession."

Holmes's infamous murder castle, known to the general public as a large hotel in the heart of Chicago, was built by a number of different contractors, as Holmes would fire them ever so often if he thought they were becoming suspicious of his true intentions for the building. The original blueprints to the hotel depict 51 doorways and at least a dozen staircases that lead to nowhere, 100 windowless rooms, two furnaces and body-sized chutes leading to an incinerator in the basement. The hotel is also rumored to have had trap doors, sound proof rooms, and at least two gas chambers. Many experts believe Holmes lured vulnerable and often lonely women into his "hotel" to torture and eventually murder them, often disfiguring and burning the bodies to get rid of evidence. He also reportedly sold the bodies of some of his victims to local medical schools, even sometimes stripping them of flesh and muscle and selling only the skeletons. The lack of bodies for Holmes's victims is a big reason why it took several years for him to be caught, and why his true body count will forever be unknown.

Holmes was also a master of insurance fraud, requiring his employees to carry life insurance policies that named him as the sole beneficiary so that he could kill them, claim they died mysteriously or accidentally, and cash out the policies. He even convinced his business partner, Ben Pitezel, to fake his own death, later killing three of Pitezel's five children when they caught on to the scheme. Holmes's many acts of insurance fraud are what eventually led to his arrest.

Holmes was tried, convicted, and sentenced to the death penalty in 1896, and died by hanging in Philadelphia just before his 35th birthday. He requested to be buried 10 feet underground and encased in concrete for a fear that grave robbers would exhume and dissect his body. Regardless of the true number of people Holmes murdered, there is no doubt that he was a truly disturbed and evil individual, and he himself even once told a reporter that he was "born with the devil inside [him]."