Investigators are trying to zero in on the Washington-area sniper with a computerized technique known as geographic profiling.
Geographic profiling, pioneered more than a decade ago by former Vancouver Police detective Kim Rossmo, works on the theory that except for a small buffer zone around their homes, criminals tend to hunt victims in areas they are familiar with.
Investigators in the Maryland case have asked Rossmo to help out.
Geo-profilers triangulate the likely home of the killer by analyzing such locations as the sites of the attacks and places where bodies were dumped. With each killing, more clues are entered into the computer.
"The more killings you have, the better it works," said Andreas Olligschlaeger, president of TruNorth Data Systems, which makes crime analysis software. "It's an unfortunate fact. More people have to die to get a better chance of capturing the killer."
While doing doctoral research, Rossmo developed a mathematical algorithm that was used as the basis for geo-profiling software now sold by the Vancouver company Environmental Criminology Research Inc. Only a few police investigators around the world have been trained on the software, which relies heavily on a detective's intuition.
The software crunches location data and other clues to create a "jeopardy surface" -- what looks like a color-coded topographical map that highlights the suspect's likeliest location.
Typically, if police believe a killer lives in a 10-square-mile area, Rossmo's tool can narrow that down to a few blocks.
Rossmo and the few geo-profilers now using his methods claim to have helped solve about half of the 450 cases they have studied.
Among those he has helped on were serial rape cases in Lafayette, La., and Mississuaga, Ontario, that were solved. Rossmo now heads research at the Police Foundation in Washington, D.C.
The Bureau of Alcohol, Tobacco and Firearms, the Royal Canadian Mounted Police, Ontario police and federal law agencies in Germany, Britain, Australia use the Vancouver company's geo-profiling software, according to ECRI.