Zahid and two of his brothers traveled to Afghanistan in the mid-1980s . His two brothers are believed to have been killed in combat . His youngest brother , Khalid Shaikh Mohammed , who was later to play a senior role in al Qaeda 's leadership arrived in 1987 . Zahid is reported to have introduced his younger brother to leading anti-Soviet fighters . According to the 9-11 Commission : The USA sought Zahid for questioning about whether he played a role in the 1993 World Trade Center bombing
1993 World Trade Center bombing
1993 World Trade Center bombing
Zahid Al-Sheikh