The chief of the Justice Department’s public integrity section, which came under fire for the botched prosecution of Senator Ted Stevens of Alaska, is stepping down from his position. The official, William M. Welch II, who became a subject of an internal inquiry into the handling of the Stevens case, will return to Massachusetts, where he was a longtime federal prosecutor, and resume his career in that role. William W. Taylor, a lawyer representing him, said in a statement Wednesday that Mr. Welch had decided to move back to Massachusetts “for family reasons.” “While the ultimate result in the Stevens...