A piece of landing gear from one of the planes that crashed into the World Trade Center has been discovered this week wedged behind a building in Lower Manhattan, police said Friday.

The part, which police believe came from one of the two commercial airliners destroyed on Sept. 11, 2001, was discovered Wednesday by surveyors inspecting the rear of 51 Park Pl., several blocks from ground zero. The surveyors called 911 to report the debris with a "clearly visible Boeing identification number," the New York Police Department...