World Trade Center site
On the morning of September 11, 2001, Islamic terrorists affiliated with Al-Qaeda hijacked American Airlines Flight 11 and United Airlines Flight 175, both which were en route to Los Angeles, and intentionally crashed them into the two main towers of the World Trade Center. The towers collapsed within two hours of the collisions. 2,606 people, including 2,192 civilians, 71 law enforcement officers, and 343 firefighters, who were in the towers and in the surrounding area died in the attacks, as well as 147 civilians and the 10 hijackers aboard the two airliners. After the collapse of the World Trade Center, hospital workers and law enforcement officers began referring to the World Trade Center site as "Ground Zero".
Siraj Wahhaj
Wahhaj was one of 170 people identified by US Attorney Mary Jo White in 1995 as "unindicted persons who may be alleged as co-conspirators" in the 1993 World Trade Center bombing, but was never charged, and denies any involvement with the bombing. 
Wahhaj was a defence witness at the trial of the Blind Sheikh, Omar Abdel-Rahman, the former leader of the Egyptian terrorist organization, Gama'a al-Islamiyya.