http://www.fbi.gov/stats-services/publications/serial-murder
"Most serial killers have very defined geographic areas of operation. They conduct their killings within comfort zones that are often defined by an anchor point (e.g. place of residence, employment, or residence of a relative). Serial murderers will, at times, spiral their activities outside of their comfort zone, when their confidence has grown through experience or to avoid detection. Very few serial murderers travel interstate to kill."
much more at link
(important note: FBI defines a serial killer as someone who has killed two or more unrelated victims/in separate crimes, IIRC)