After the 1993 World Trade Center bombing took place, his research area changed to terrorist attacks. In the following years he was involved with the research of the 1998 United States embassy bombings in Tanzania and Kenya, the 2000 USS "Cole" bombing in Aden, Yemen, and the destructive attacks of September 11, 2001, on the World Trade Center and The Pentagon. In course of the years he therefore became an expert on al-Qaeda.