In this file photo of Feb. 26, 1993, helicopters jockey for position over the World Trade Center in New York following a noontime blast, which rocked the
In this file photo of Feb. 26, 1993, helicopters jockey for position over the World Trade Center in New York following a noontime blast, which rocked the twin towers complex. Twenty years ago a group of terrorists blew up explosives in an underground parking garage under one of the towers, killing six people and ushering in an era of terrorism on American soil. ((AP Photo/Ron Frehm, File))