WASHINGTON (Reuters) - FBI officers raided a House of Representatives office building on Saturday night, and NBC television said it had searched the offices of Louisiana Democratic Rep. William Jefferson. The Federal Bureau of Investigation confirmed the unusual raid at the Rayburn House Office Building on Washington's Capitol Hill but would not say whose office was searched. "Agents of the FBI's Washington field office executed a search warrant this evening at Rayburn at approximately 7:15," Debbie Weierman, a spokeswoman for the FBI's Washington field office, said. Weierman said the search warrant was sealed and she could not confirm whose office...