The investigation into an alleged plot to bomb the city's subway moved forward on several fronts Friday as a third suspect was arrested in Iraq and authorities looked into whether a fourth person had traveled to New York as part of the scheme, officials said. A law enforcement official familiar with the case said the man's trip to New York was described by an informant who had spent time in Afghanistan and proved reliable in past investigations. "He's been a source of multiple correct information in the past," the official said, speaking on condition of anonymity because of the continuing...