Minnesota Public Radio has obtained the FBI record of the late Senator Paul Wellstone of Minnesota, who died in a plane crash eight years ago this week. The records show the FBI first tracked Wellstone in 1970 after he was arrested at an anti-Vietnam War protest. The records might also raise new questions about the plane crash that killed Wellstone, his wife, his daughter and three staffers. The National Transportation Safety Board determined the crash was caused by pilot error, but the FBI documents reveal for the first time that specific criminal leads were pursued by investigators. Part of the FBI probe focused on problems with the plane’s de-icing equipment. A caller from Florida said members of the American Trucking Association had planned to disconnect the plane’s de-icing equipment because they were upset with Wellstone’s efforts to expose organized crime in the trucking industry. The FBI files also reveal that Wellstone’s St. Paul office received a threatening postcard the day before the plane crash.