One in a million? Heh.
Many more hidden sociopaths walking the streets every day. Not every sociopath is emotionally unstable. Psychological tests are superficial for general population, I've passed with flying colors every time. Easy to fool person who can't wait to end shift and go home, thinking how most people are just right in the head and don't need to be thoroughly checked. If we are talking about highly intelligent sociopath, you need expert to deal with him/her. Regular psychologist/psychiatrists won't cut it, intelligent people can easily fool those less intelligent than them.
Especially with digital age, came also age of introverts and shut-ins who successfully fake social skills.
Also, not every sociopath has to be violent, to kill people. Most of them at some point do commit murder, but there could pass decades before that happens. Modern society allows different mechanisms to abuse people, aside from physical violence.