Federal prosecutors have opted not to seek criminal charges against William M. Bulger, concluding a six-year investigation into whether Mr. Bulger, a former president of the University of Massachusetts system, obstructed efforts to capture his mobster brother, James (Whitey) Bulger, The Boston Globe reported today. William Bulger, who also was a longtime president of the State Senate, resigned his university post in 2003, in part because of public criticism over his role in the federal investigation. Citing insufficient evidence to seek indictments, the U.S. attorney’s office in Boston let expire a federal grand jury investigating whether Mr. Bulger had committed perjury or obstruction of justice, the newspaper reported. —Karin Fischer