A group of terrorists affiliated with al-Qaeda parked a yellow rental van in the basement of the WTC containing a 1,500 lbs urea-nitrate bomb. The bomb detonated at 12:18 p.m. on February 26, 1993 killing 6 people and injuring more than 1,000. The bomb made a hole 200 feet wide and seven stories deep in the tower.
It is believed that the Terrorists chose the Twin Towers to attack because of the buildings being emblematic of Americas strength. It was also chosen because there could be many casualties with such a large building with many inhabitants.