I read this amazing article about the neuroscience involved in the mind of a serial killer and it proposed this interesting theory of how two minds exist inside a serial killer.
Read on more to find out:
https://blog.oup.com/2021/04/what-can-neuroscience-tell-us-about-the-mind-of-a-serial-killer/#:~:text=One%20explanation%20for%20such%20cognitive,the%20most%20unspeakable%20and%20violent