Second, although both types of killers evoke fear and anxiety in the community, the reaction to a mass murder will be much more focused and locally limited than that to serial killing. People generally perceive the mass killer as one suffering from mental illnesses. This immediately creates a "they"/"us" dichotomy in which "they" are different from "us" because of mental problems. We can somehow accept the fact that a few people go "crazy" sometimes and start shooting others. However, it is more disconcerting to learn that some of the "nicest" people one meets lead a Dr. Jekyll and Mr. Hyde life: a student by day, a killer of coeds by night; a caring, attentive nurse who secretly murders sick children, the handicapped, or the elderly; a building contractor and politician who enjoys sexually torturing and killing young men and burying them under his home. When we discover that people exist who are not considered to be insane or crazy but who enjoy killing others for "recreation," this indeed gives new meaning to the word "stranger." Although the mass murderer is viewed as a deranged soul, a product of a stressful environment who is just going to "explode" now and then (but of course somewhere else), the serial murder is seen as much more sinister and is more capable of producing fear.
http://www.serialhomicide.com/serial-killers.htm
