Serial killers of women usually have long-held and highly developed violent sexual fantasies, and their victims are the subject of their lust, according to experts.

While little is known about what triggers the fantasies, many experts believe their specific content starts with something the killer saw as a child, conversations he overheard, or from movies, television or photographs.

"The fantasies become elaborated over time and new bits and pieces are added depending on the intellectual capacity of the person," said Park Dietz, a forensic psychiatrist who recently completed a study of sadistic killers. The more intelligent men are "like film directors with well-advanced scripts," he said.

Eight women police have identified as prostitutes have been slain in the Washington area in the past 14 months. On Sunday, Arlington police arrested Chander "Bobby" Matta, a 21-year-old with no criminal record, in the death of prostitute Sherry K. Larmen. Arlington Police Chief William K. Stover said police have physical evidence and statements from Matta also linking him to the deaths of Jodie Marie Phillips, 16, and prostitute Sandra Rene Johnson, 20.

District police say they have evidence linking at least two of the other killings and are seeking another suspect in those deaths.

For 30 years, as serial killings appeared to increase in the United States, psychologists, anthropologists, sociologists, neurologists and others have dissected the fantasies and addictions of these men. Scientists have analyzed the men's childhoods and examined their parents and have tried to find a culprit in a part of their brains or their body's chemistry.

They have interviewed convicted murderers in their jail cells, many of them on death row, and have spent countless hours with parents, friends and other scientists trying to discover what kind of man commits these crimes and why.

Most people who have violent fantasies never commit crimes, Dietz noted, because they are inhibited by their conscience, their morals or the threat of legal consequences. The experts do not know why others overcome these barriers and lash out violently. "We're not very good at explaining the whys of human behavior," said Janet Warren, an assistant professor at the University of Virginia's Institute of Law, Psychiatry and Public Policy. "What we've all been doing is to describe what these people are like."

Experts believe that prostitutes may become the target of serial killers for several reasons, including that fact that they are easy targets. The killer may believe that there will be less pressure on police to solve the crime and that a prostitute's death might not be quickly discovered because she lives on society's fringes.

The oldest, and now much-disputed, theory on why killers attack prostitutes is known as the "Madonna-Whore Complex," in which a murderer who grew up with a mother he believed was promiscuous divides the world into good and bad women, and kills or rapes the bad.

A more commonly held theory, said Dietz, is that an impotent man goes to a prostitute hoping to be cured and becomes outraged at her when he is not. "From their own frustration, anger, or, from time to time, ridicule from the prostitute, he becomes enraged and kills her," he said.

Anthropologist Elliott Leyton, author of "Hunting Humans," a book about serial killers, said prostitutes can be the easiest targets for men who hold women responsible for their own failings, professional or personal.

"They begin to start having fantasies about the group that denied them access," said Leyton. "In an important sense, {sexual homicide} is similar to rape because it's a fundamental way of humiliating your victim."

In the United States, women are a common scapegoat for men's failures, Leyton said.

"As long as we reduce people to sex objects and validate violence, we're going to continue to have these problems," he added.

Fred Berlin, director of the Sexual Disorders Clinic at the Johns Hopkins Hospital, said he believes violent fantasies turn into abnormal cravings in these killers.

"The intensity of the craving is such that it is too painful not to satisfy it," said Berlin, who examined Randy Breer, the Dale City carpenter who sexually assaulted three Northern Virginia girls and a young woman.

Serial killers have murdered middle-class women, poor women, children and other men. Some have claimed they suffered delusions and were ordered by visions or voices to kill.

In the most exhaustive study of serial killers to date, agents and others working at the FBI's Behavioral Science Unit in Quantico, interviewed and analyzed the cases of 36 convicted sexual killers. All were male, most were white and three-quarters had average or above-average intelligence.

The study, which is used by law enforcement authorities to better read the psychological clues left at the crime scene, found that drug or alcohol abuse was a major problem in the men's families.

Over half came from families whose members had criminal histories and some psychiatric disorders. Over 40 percent lived outside their parents' homes before age 18 and had been in foster care, state homes, detention centers or mental hospitals.

Many of the killers exhibited violent behavior in their youth, such as killing animals, and they viewed themselves as loners.

"Perhaps the most interesting result was that most offenders said that they did not have a satisfactory relationship with the father and that the relationship with the mother was highly ambivalent in emotional quality," the authors wrote in the 1988 book, "Sexual Homicide."

Almost half reported an aversion to sex. Generally, they did not succeed in the endeavors they attempted in school, on the job or in military service.

To compensate for their failures, most had fantasies that they were able to control, the authors wrote. Others went out of control. "What makes one person step over the line and someone else not, you will never know," said FBI agent Robert K. Ressler, one of the book's authors.

Warrent said she has interviewed killers who described how the fantasy became reality. First they thought about strangling a victim, then carried around rope in a car trunk for years. Years later, they followed women with no intent of approaching them. Then they murdered.