Experts who study serial killers say the Washington-area sniper, unlike most serial killers, kills from long distance because he is more interested in causing widespread terror in the community than he is in getting to know his individual victims.
The gunman in Maryland and Virginia is a "spree killer," someone who kills several people in a small window of time, experts believe, as opposed to a serial killer, who may space his killings over months or years, or a mass murderer, who kills many people all at once.
Charles Patrick Ewing, a professor of law and psychology at the State University of New York at Buffalo, said the sniper, who has used a rifle at distances of more than 100 yards to slay nine victims and wound two others, appears to be more like the anonymous attacker who mailed last year's anthrax-laced letters.
The anthrax attacks "were driven by the desire to terrorize the community, and the person who mailed the letters didn't appear to really care about who died as a result of them."
"I don't recall a case like this where the murders have been committed at such a distance," Ewing said. "It is so impersonal. That's what leads me to believe that it isn't really the same sort of sexually based type of crime as a serial murder."
Classic serial homicide theory is based on sexual motivation, and the killer often stalks or tortures the victim and kills at close range.
The classic view is spelled out by Robert Ressler, a former FBI agent who pioneered psychological profiling and conducted face-to-face interviews with such infamous killers as Jeffrey Dahmer, David Berkowitz and Ted Bundy.
"To a man, they (serial killers) were dysfunctional sexually," Ressler wrote in his 1992 book, "Whoever Fights Monsters." "They were unable to have and maintain mature, consensual sexual experiences with other adults, and they translated that inability into sexual murders."
Ewing said most classic serial murderers "obtain some sort of sexual satisfaction from the crime. It seems to come from the act of violating the victim. That doesn't seem to be the case with this one. In my estimation, what is driving this one is less the individual killing than the terrorizing of the community."
Brent Turvey, a professional profiler from Sitka, Alaska, and author of the textbook "Criminal Profiling: An Introduction to Behavioral Evidence Analysis," agrees that the Washington-area sniper is different from classic serial murderers.
"Those comparisons are completely inappropriate," Turvey said.
"The reason why everybody is making those comparisons is because they are all talking to the retired profilers who made those kinds of cases in the 1970s."
Turvey said he believes this sniper is more like Andrew Cunanan, who killed five people, including designer Gianni Versace, during a cross-country rampage in 1997.
"Cunanan was a classic spree killer," Turvey said. "A serial killer will kill multiple people on multiple dates with a . . . cooling-off period in between. A spree killer will kill a bunch of people in a very narrow window of time.
"Most of these Maryland area crimes occurred in a very short period," Turvey said. "He did his killing, then went home to watch the coverage on TV."