How many people does the average serial killer kill?

i know it has to be atleast 3, with a cooling off period, but how many does the average serial killer kill in his life? and do any ever.. stop? without getting caught, or do they kill for life if they never get caught? how common are serial killers?

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).