Shadowy Trio Seen Studying Sears Tower
CHICAGO, March 16 (UPI) -- U.S. federal officials have confirmed they are investigating an incident where three men were seen studying and taking pictures of Chicago's Sears Tower.

The men were spotted outside the 110-story building by security guards about three weeks ago. The men were questioned and allowed to leave, but the guards notified the Chicago Police Department. They in turn notified the Joint Terrorism Task Force, the Chicago Tribune reported

The guards recorded the car's license plate and it was traced to a rental agency, which said the car was returned about an hour after the incident.

It was later determined it had been rented with a fictional name, sources told the newspaper.

Also within the last three weeks, WLS-TV reported a man was questioned about sketching the Boeing World Headquarters building.