They were former classmates at a New York high school, both on a mission to join the Taliban and fight U.S. forces in Afghanistan. But when Zarein Ahmedzay and Najibullah Zazi arrived in Pakistan in the summer of 2008, two high-ranking al-Qaida operatives gave them another set of marching orders. "They told us we would be more useful if we returned to New York City ... to conduct operations," Ahmedzay said Friday in a guilty plea that offered more chilling details of a foiled plot attack on the New York City subways last fall. Asked by a judge in federal...