The Supreme Court's recent ruling overturning the warrantless use of GPS tracking devices has caused a "sea change" inside the U.S. Justice Department, according to FBI General Counsel Andrew Weissmann.

Mr. Weissmann, speaking at a University of San Francisco conference called "Big Brother in the 21st Century" on Friday, said that the court ruling prompted the FBI to turn off about 3,000 GPS tracking devices that were in use.

These...