From a young age, Jemma Lilley was obsessed with serial killers. It was a disturbing fascination her family dismissed as harmless. She was hooked on horror movies, wrote about serial killers, even dressed like some of the world’s most infamous murderers. As she grew older, her unusual fixation on brutal violence and the macabre only intensified. And by the age of 23, Jemma’s thirst to kill was overwhelmingly strong. Sadly, teenager Aaron Pajich-Sweetman would be her first victim. Steve Pennells investigates what drove Jemma to become a killer.