Doctors and nurses who have taken oaths to save life and help others can be killers. Highly educated people can be very dangerous killers as well as poorly educated people. People who appear to be happy and successful can be killers. Atheists and regular churchgoers can be murderers. People kill because they enjoy it, because it can be sexually and intellectually exciting, and because it can be just plain old profitable.
Some people kill all by themselves and others engage partners in their efforts.
Some are fortunately caught quickly while others elude the police for years and some are even never caught. It tells us that who amongst us will be the next murderer is impossible to predict. It tells us that everyone should be a suspect. However, a careful study of murderers also tells us that a logic is involved in every killing. To make sense of the murder is often the quickest route to finding out who committed the murder.