State attorneys general working to determine whether Comcast Corp’s deal to buy Time Warner Cable Inc is legal have expanded their investigation to include AT&T Inc’s plans to buy DirecTV, according to sources close to the merger probe. Justice Department to interview critics and proponents of the Comcast merger, which some lawmakers and public interest groups fear will result in higher costs and less competition. The states have now broadened their focus to include AT&T’s $48.5 billion proposed deal for DirecTV, the No. 1 U.S.