I love reading about serial killers, so much so I'm gonna limit myself to two.
The first is Andrei Chikatilo, a serial killer/rapist who lived in the Soviet Union. He could only get sexual satisfaction from the act of killing, and he killed a lot; he was convicted for 52 murders though he claimed to have killed at least 56. And he killed everyone: young girls, young boys, older women. And he got away with it for so long ironically because of the Soviet police's brutal methods. They would never suspect him and instead go after someone else, and because they were the Soviet police, they would force confessions out of these unrelated suspects. They finally managed to get him, and he was sentenced to death. He was ultimately executed via a bullet to the head, the most Soviet way to execute a criminal if you ask me.
The second is Richard Chase, aka the Vampire of Sacramento. He was a confirmed schizo that went way off the deep end when he decided to stop taking his meds. He began consuming the blood of animals such as rabbits and dogs under the belief that his heart was shrinking. He also started entering people's homes if their doors were unlocked; he believed if they were locked, he wasn't welcome. Chase entered two houses, the first one he murdered a young woman and the second he killed 4 people. Chase was fucking sadistic too; he would do unspeakable things to his victims, one of which was a 22-month old. I'll spare everyone the details, but this motherfucker is the sickest killer I've ever read about. He was eventually arrested and committed suicide via overdose on medication. During the autopsy, they found that his heart was at a perfectly healthy size.