1. Jeffrey Dahmer, nicknamed the "Milwaukee Cannibal," murdered, cannibalized, and dismembered 17 men and boys.
2. The Zodiac Killer, who potentially murdered up to 37 people in California and Nevada, has never been identified. The killer sent several cryptograms to the local press, but only one has ever been solved.
3. Luis Garavito, nicknamed "The Beast," confessed to killing 147 boys, ages 6 to 16, over a seven-year period in Colombia.
4. Gary Ridgway, also known as "The Green River Killer," targeted sex workers from Seattle and was convicted of killing 49 women.
5. Ed Gein, nicknamed "The Butcher of Plainfield," dug up corpses from graveyards and created keepsakes out of their bodies.
6. Belle Gunness killed her boyfriends, husbands, and even her children. She would then collect her victims' life insurance and any other valuables they had.
7. Pedro López confessed to killing 300 young girls, but the true total remains unknown. Despite being one of the most notorious serial killers of the 20th century, he was released in 1998 and his current whereabouts are unknown.
8. Tsutomu Miyazaki, nicknamed "Dracula Miyazaki," killed four little girls. He earned his nickname because he drank the blood of one of his victims.
9. Ted Bundy confessed to murdering 30 young women in the 1970s. Even after his confession, his total victim count still remains unknown.
10. Harold Shipman, known as "Doctor Death," is believed to have killed 250 people. He injected heroin into his patients and then falsified their medical records.
11. Dean Corll, nicknamed "The Candy Man," murdered 28 young boys in Texas. His family owned a candy store and he would lure his victims in with sweet treats.
12. Frederick Mors killed eight elderly patients in New York. He was sent to an asylum, escaped, and was never caught.
13. Jane Toppan, nicknamed "Jolly Jane," was a nurse that confessed to poisoning 31 patients. After overdosing them, she would get in their beds and lie with them as they died.
14. Between killing his mother at age 13 and his wife and niece at age 47, Charlie Brandt is also linked to 26 unsolved murders in the state of Florida.
15. Aileen Wuornos shot seven men to death in Florida while she was working as a sex worker
16. Juan Corona was convicted of murdering 25 migrant farm workers. He buried his victims in a fruit orchard in California.
17. Charles Cullen, nicknamed "The Angel of Death," poisoned his patients with unprescribed medication. It's believed that he contributed to the deaths of over 400 people.
18. Andrei Chikatilo, nicknamed "The Red Ripper," confessed to torturing and killing 56 women and children in the Soviet Union.
19. Alexander Pichushkin, known as "The Chessboard Killer," targeted homeless men who he lured to his home with vodka. He killed at least 48 people and initially said he wanted to complete the number of squares on a chessboard and kill 64 people.
20. John Wayne Gacy, nicknamed the "Killer Clown," dressed up as a clown and killed 33 young boys and men. Some of his victims were buried in the crawl space of his home in Chicago.
21. And finally, Jack the Ripper killed numerous young sex workers in London by slashing their throats and removing their organs. The killer's identity remains unknown to this day.
Norman Bates' name was misspelled in an earlier version of this post.