UCSON, Oct. 28 — Officials building a case against the Washington-area sniper suspects are using a new investigative tool to help trace their movements across the country. It is an Internet-based system called Coplink, developed at an artificial intelligence laboratory here, that allows police departments to establish links quickly among their own files and to those of other departments.

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During the 21 days in which snipers terrorized the area, investigators used everything from specialized ballistics testing to geographic and criminal profiling to radio and television announcements to track them down. Then, in what turned out to be the 11th hour of the pursuit, they finally reached out to Coplink. As it turned out, John Muhammad and Lee Malvo were arrested before it was fully installed, but now the post-arrest task force is using the system to help connect the dots.

All of the information that was collected — including that from other computer database systems like the Federal Bureau of Investigation's Rapidstart — is now being downloaded into the Coplink database so that the accumulated data can be compared, said Robert Griffin, president of Knowledge Computing Corporation of Tucson, which is turning the prototype in the laboratory into a commercial product. "The more data you get, the better Coplink works," he said.

Coplink was designed by Hsinchun Chen, the director of the Artificial Intelligence Laboratory at the University of Arizona. "It's the Google for law enforcement," he said, referring to a speedy popular Internet search engine that, given a couple of words, can find an array of related Web sites. "Things that a human can do intuitively we are getting the computer to do, too."

During the sniper investigation, which generated hundreds of thousands of tips, the number of potential clues to assimilate was daunting. "We were mobilizing a massive effort," said Lt. Mitch Cunningham of the Montgomery County police. "We had tactile resources, the military, federal, state and local law enforcement agencies and information technology using several products where each one of these had a role." So when the National Institute of Justice, the Justice Department's research and development arm, suggested that the sniper task force try Coplink, the officials agreed.

While no one is suggesting that old-fashioned detective work is being replaced by machines, the idea behind Coplink is to provide a computer program that can save busy police officers precious time and sometimes even help solve cases. That's something Coplink's oh-so-human advocates will boast about like a good story about a rookie getting a lucky break in a case. It is like having a new partner in the form of a computer backing up a cop.

"There is a greater and greater role for technology in law enforcement," Lieutenant Cunningham said.

Software like Coplink's is already part of everyday life, said Rodney A. Brooks, director of the Artificial Intelligence Laboratory at the Massachusetts Institute of Technology. "It's inevitable that it's going to have some law enforcement application, too."

Mr. Brooks said that his company, iRobot, has machines that investigate caves in Afghanistan before military units enter and that such machines are finding their way into municipal police forces. "Columbine High School is a great example of how the police did not know what was going on inside," he said of the 1999 school shootings in Colorado.

Furthermore, he said, the human mind can process and retain only so much information. "There are enormous amounts of facts and connections out there, more than can be held in any one person's mind," he added. "Just like with gene patterns, it's much too complex for someone to remember it all."

Coplink works by linking and comparing data from new and existing files. For example, Mr. Griffin said, in a Tucson case a man was found lying face down after his throat had been cut and he had been run over by a vehicle. The man was still alive, and before he was taken to a hospital he told people at the scene, "Shorty did it." The name Shorty was put into Coplink and cross-referenced with the victim's personal data, and within minutes the records showed that the two men had been in prison together.

The program also allows users to look at lists of data or to create graphs and charts showing affiliations among different criminals.