If you're interested in this exact process being expanded upon, do yourself a favour and watch the excellent Netflix show featured above. If you've watched/enjoyed/liked that Jeffery Dahmer shyt they released recently, then you owe yourself to watch it as penance for enjoying sensationalized Cac depravity.
Also, chemical imbalances aren't necessarily the cause when it factors into the sadistic minds of Serial killers/rapists. It almost always stems from upbringing in the worst circumstances that allows such neurological behaviours to manifest and then subsequently flourished, hence why they started to look for 'patterns' with regards to how these new 'killers' came about that differentiated them from ordinary, one off, murderers.
Is that an Alfred Hitchcock Biggie Smiley?