"The big story is the privacy law that protects your e-mail does not protect your Google search terms," said Orin S. Kerr, a professor at the George Washington University Law School and a former lawyer in the computer crime section of the Justice Department.
Other lawyers argue that the law that provides protection for e-mail content, or even the Fourth Amendment protection against unreasonable searches, could be applied to data about Web searching, but the issue has not been tested in court.
The break in the St. Louis murders came in 2002, when a reporter received an anonymous letter with a map generated by Microsoft's MSN service — marked with the location where a body could be found.
The F.B.I. subpoenaed Microsoft for records of anyone who had searched for maps of that area in the days before the letter was sent. Microsoft discovered that only one user had searched for precisely that area and provided the user's Internet Protocol address. That address, in turn was provided by a unit of WorldCom, which identified the user as Maury Troy Travis, a 36-year-old waiter. (Mr. Travis was arrested and hanged himself in jail without ever admitting guilt.)
While requests for search data have been few, computer experts expect them to increase.
"It is rare that those links will be a slam-dunk that will make a case," said John Curran, a former cybercrime investigator for the F.B.I. "But when you are putting together a larger case, you are trying to connect the dots, and it is the little things that actually help."
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