PROVIDENCE — Raymond D. “Beaver” Tempest Jr. served more than 23 years in prison for a murder he insists he did not commit. And now he is using a judge’s conclusions — that investigators coached a string of questionable witnesses and concealed evidence to secure his conviction — in a lawsuit filed late Thursday in U.S. District Court. Tempest is suing retired Woonsocket Sgt. Ronald Pennington, former Woonsocket Police Chief Rodney Remblad and the City of Woonsocket for their roles in what he argues was his wrongful conviction in the 1982 bludgeoning death of Doreen C. Picard, a 22-year-old former prom queen from Bellingham, Massachusetts.