These days, modern forensics and focused police work make it harder to murder people in mass numbers. But back before the 1900s, a clever killer could escape notice for years, just as H.H. Holmes did. He's considered one of America's first recorded serial killers.
Holmes grew up in a wealthy family and at an early age showed in interest in medicine. Out of curiosity, he'd perform rudimentary surgeries on animals. He was also crooked. In medical school, he stole cadavers and used them for insurance scams. Holmes eventually moved to Chicago to run a pharmacy. The business was a front for a horrific life.
He constructed a three-story brick building and lured young women inside, where they met terrible deaths from suffocation, hanging and incineration. Sometimes Holmes sold parts of the bodies to medical schools; other times he'd use them for his tried-and-true insurance fraud scams. Still other bodies were simply dumped in his basement.
Eventually, it was the fraud that did Holmes in. After capturing him and questioning several people, police decided to search Holmes house. What they found was a bizarrely constructed "murder mansion" full of dead-end staircases, secret passageways, oddly shaped rooms and other strange construction. There were also soundproof rooms and metal-covered walls equipped with blowtorches, all for torturing victims.
Holmes was sentenced to death and confessed to murder, but no one really knows the grisly toll of his crimes. Only nine murders were confirmed, but estimates range from 20 to 200. No matter the final tally, Holmes was a prolific killer with a devious imagination that led to his execution in 1896.