The well-advanced plot to blow up airliners flying from Britain to the United States had the markings of al-Qaida, and it’s not yet certain that authorities have found everyone involved, the Homeland Security secretary says. More will be learned in the next hours and days, Secretary Michael Chertoff told reporters Thursday. In the meantime, the U.S. airline system remains on high alert, with tougher passenger inspections expected Friday. Full Story