For Errol Morris, cameras never stop rolling Filmmaker already has grand legacy, but he is focused on future ← Related Article Visit The Boston Globe Share on Twitter Share on Facebook Comment on this Scroll to top of page John Tlumacki/Globe Staff Errol Morris is a Boston institution and a national treasure for the documentaries he has made during the past 30 years. Mark Lipson/Miramax Films 1988’s “The Thin Blue Line” freed an innocent man from prison. Claire Folger/Associated Press 2003’s “The Fog of War,” in which Robert McNamara broods over his part in the Vietnam War, won an Oscar. Sony Pictures Classics 2008’s “Standard Operating Procedure” probed the nature of photography and the sins of Abu Ghraib. New Yorker Films “Gates of Heaven” (1978) remains the greatest film about pet cemeteries ever made. Now, he is putting the finishing touches on “The Unknown Known,” a documentary on former Secretary of Defense Donald Rumsfeld. Drafthouse Films The most important thing Morris may do this year is put his name on “The Act of Killing,” which opens in the area on Friday.