The image of the evil genius serial killer is mostly a Hollywood invention. Real serial killers generally do not possess unique or exceptional intellectual skills. The reality is that most serial killers who have had their IQ tested score between borderline and above average intelligence. This is very consistent with the general population. Contrary to mythology, it is not high intelligence that makes serial killers successful. Instead, it is obsession, meticulous planning and a cold-blooded, often psychopathic personality that enable serial killers to operate over long periods of time without detection.
That’s a myth
https://www.scientificamerican.com/article/5-myths-about-serial-killers-and-why-they-persist-excerpt/