Wikipedia
Although not yet a teenager, Mary Bell was assisted in her crimes by her best friend of 13 years, Norma Bell, who was completely unrelated despite having the same last name. Together, the couple strangled two young children, ages three and four. When the police investigated Mary’s background, they discovered that her prostitute mother was abusive. She on more than one occasion tried to kill Mary and forced her to have sex with men.
While Norma was acquitted of the crimes due to her feeblemindedness, Mary served 12 years in a juvenile detention center. Today she is a grandmother and lives anonymously with a new name.
4. William Heirens – 18 years old
William Heirens began committing petty crimes at the age of 13, but five years later he turned to murder. After brutally stabbing his second female victim, he wrote a message on the wall in lipstick. He would say, “For God’s sake, catch me before I kill more. I can’t control myself.” Sadly, he would murder a six-year-old girl before the police finally caught up with him.
Heirens served 65 years in a Chicago prison before dying of natural causes.
