MIAMI (AP) - An agitated passenger who claimed to have a bomb in his backpack was shot and killed by a federal air marshal Wednesday after he bolted frantically from a jetliner that was about to take off, officials said. No bomb was found. The man, identified as Rigoberto Alpizar, a 44-year-old U.S. citizen, was gunned down on a jetway just before the American Airlines plane was about to leave for Orlando, near his home in Maitland. It was the first time since the Sept. 11 attacks that an air marshal had shot at anyone, Homeland Security Department spokesman Brian...