With no solid leads in their hunt for a sniper who has gunned down eight people in the Washington, D.C., area, investigators have turned to a relatively new technological tool: geographic profiling.

Barring a lucky break, the technology currently seems like the police's best chance to find the shooter, who has killed six, left millions on edge, and single-handedly lowered the attendance rate in Maryland suburban schools.

The technique, first used in 1990, operates on the assumption that a serial murderer (or rapist) balances his desire to kill far from home to avoid being recognized with his desire to be in familiar territory. The tension between these two desires usually means that serial killers kill close to home, but not too close, leaving a "comfort zone" around their home that can be detected mathematically, according to Dr. Kim Rossmo, the technique's pioneer.

A 13-year-old boy, the sniper's eighth victim, was shot outside Benjamin Tasker Middle School.

Investigators into the Maryland shootings have good cause to be hopeful about geographical profiling's potential. A software program that Rossmo developed called Rigel — the only professional geographic profiling software currently available — has in past cases pinpointed a criminal's home within a few blocks. On average, according to Rossmo, the program narrows the police's target area by 95 percent.

The program generates a two or three-dimensional map, a "jeopardy," which shows the probable site of the criminal's home based on where the victims' bodies were found. The profiler, using his own experience, can also incorporate the location of other relevant evidence not found at the scene of the crime, like the gutter where the murder weapon was discarded or the public park where the victim's purse turned up.

But while geographic profiling could help an investigation, it can't point directly to the perpetrator. Even Rossmo warns against seeing geographic profiling as a solve-all investigative device. He has described it as an information management tool that gives police a way to better allocate their time and money.

Rossmo has explained that geographic profiling can never solve a case alone. It can only help focus the investigator's search by pointing them in a direction most likely to produce tangible evidence or leads to the criminal.

Rigel works best when used by an experienced geographic profiler on a serial criminal who fits a specific profile. According to Ian Laverty, an engineer who helped develop Rigel and president of Environmental Criminal Research Incorporated, the firm that produces it, the software specializes in "hunters" — criminals who leave their home base already planning to find a victim.

"A hunter works from a homesite and travels out with a purpose of finding a victim and a location to commit the crime," said Laverty. "So [to best use Rigel] we must look at the nature of the crime and see if it is a hunter pattern."

But not all serial killers are hunters. In his textbook on geographic profiling, Rossmo, now research director of the Police Foundation in Washington D.C., defines four other types: trappers who lure their victims to them; stalkers who follow their victims; poachers who travel away from home to hunt; and trollers who perpetrate crimes opportunistically while in the midst of other activities.

While not enough is publicly known about the Maryland shooter to determine his methodology, Rossmo believes that all criminals commit their first crimes close to home, only leaving the areas that they know as they gain confidence. By this logic, even if the shooter at large now modifies his behavior and expands his target zone, his first six shootings, all of which occurred within a five-mile area in Maryland, probably point toward his home.

Of course, by the time the profile emerges, the killer could have moved. But if geographic profiling leads to the location of his former base of operations, even that would be a huge boost to the Maryland investigation.

In the summer of 1998, Rossmo assisted an investigation of a Lafayette, La., serial rapist who had attacked as many as 15 women in the area over a period of 11 years. After reading an article on geographic profiling, Major Jim Craft of the Lafayette police, who led the task force devoted to the criminal, invited Rossmo to help out. His geoprofile, which he sent to Craft after one or two months , allowed police to narrow the areas they patrolled.

"It was helpful to prevent further attacks," Craft said. "Previously there was a pretty large area that we had to focus on to make sure we didn't have any further attacks. As a result of that profile we were able to narrow down our geographic area and focus our resources from an area of 60,000 people to a location with about 30,000 people in it."

Although the geoprofile accurately predicted the killer's home area, the information did not end up helping them capture him. The case was solved when the police received an anonymous tip with the rapist's name. At the time of his arrest, the rapist had moved outside the area Rigel predicted.

Still, Craft and the Lafayette Police Department were impressed with geographic profiling.

"It's not going to specifically identify a perpetrator but it will help you focus your investigative efforts and narrow down or eliminate information from other areas," Craft said.

Whether Rigel will help in finding the Maryland shooter remains to be seen, but some proponents think it can be useful for more than serial murders.

Says Laverty, "The technique itself is applicable to all types of serial crimes like robbery, burglary and arson."