H.H. Holmes is said to have murdered between 20 and 100 people in his twisted “Murder Castle” in the 19th century. He was first serial killer in American recorded history to be caught and imprisoned for his crimes, but he wasn’t the last. Other killers such as The Zodiac Killer, The Golden State Killer, and the Uber Serial Killer followed in his footsteps. Some were caught, some still remain, but they will all send shivers up your spine with their horrific crimes.