"A little-known but powerful government database, which had featured information on millions of Americans, is no more. The Justice Department created the pilot project, which went by the contrived acronym of MATRIX (Multistate Anti-TeRrorism Information eXchange), and made it available to state and local police starting in 1998.

Data was provided by Seisint, a data-mining firm recently embroiled in a flap over an intrusion into its databases that may have compromised the information of about 310,000 Americans. Seisint is owned by Lexis-Nexis.

Among the databases MATRIX tied together: criminal history, prisoner and sex offender information, driver's license and registration data, and many other databases such as court records and directory assistance listings. MATRIX permitted police to run complex queries, such as "all red Buicks with 7 as the last character in the license plate."