"A serial killer is typically defined as an individual who has murdered three or more people over a period of more than a month, with down time (a "cooling off period") between the murders, and whose motivation for killing is largely based on psychological gratification... Often, a sexual element is involved with the killings, but motives for serial murder include "anger, thrill, financial gain, and attention seeking." The murders may have been attempted or completed in a similar fashion and the victims may have had something in common; for example, occupation, race, appearance, sex, or age group." - Wikipedia