The government has refused to open its files about what, if anything, moved across the sky and crashed in the woods near Kecksburg, Pa., 40 miles southeast of Pittsburgh.
Traffic was tied up in the area as curiosity seekers drove to the area, only to be kept away from the crash site by soldiers.
The Air Force's explanation for the unidentified flying object: a meteor or meteors.
"They could not find anything," one Air Force memo stated after a late-night search on Dec. 9, 1965. Several NASA employees also were reported to have been at the scene.
Eyewitnesses said a flatbed truck drove away a large object shaped like an acorn and about the size of a Volkswagen bus. A mock-up based on the descriptions of local residents sits behind the Kecksburg Volunteer Fire Department.
UFO enthusiasts refused to let the matter die and journalist Leslie Kean of New York City sued NASA four years ago for information.
"This is about the public's right to know," Kean said. "We would be doing this lawsuit regardless of whether UFO groups were interested in it or not. It's a freedom of information issue."
The agency has turned over several stacks of documents which Kean says are not responsive to the request, an argument that U.S. District Judge Emmet Sullivan agreed with.
In March, Sullivan rejected NASA's request to throw the case out of court, resulting in negotiations that led to the agency promising last week that it will conduct a more comprehensive search.
Kean said Friday that she sued NASA rather than the Army because the space agency a decade ago released some relevant documents on the case.