"But the FBI also withheld numerous files, saying they were exempt from the Freedom of Information Act, including part of a surveillance report on a December 1971 antiwar rally in Michigan. There, Lennon urged the release of activist and singer John Sinclair, who was serving a 10-year sentence for possession of two marijuana joints. A judge soon freed him."
I was at that event and would find that file very interesting. Makes me wonder what is in my file up in FBI headquarters.