Accused terror plotter Najibullah Zazi pleaded guilty Monday, admitting he and others were on the verge of carrying out "martyrdom operations" in Manhattan subways. Appearing in Brooklyn Federal Court, Zazi said the transit attacks were planned for Sept. 14, 15 or 16 - days after the eighth anniversary of the 9/11 terror attacks. He and his co-conspirators aborted the ghastly plot after Zazi's car - packed with chemicals and detonators - was stopped on the George Washington Bridge by investigators who had tailed him from Denver. "I realized law enforcement was watching," Zazi, 25, said matter-of-factly in court. Sources said...