According to a Senior Executive Intelligence Brief titled, ‘Terrorism: Bin Ladin Determined to Strike in the US’ on August 7, 2001: “His [Bin Ladin’s] attacks on the US Embassies in Kenya and Tanzania in 1998 show that he prepares operations years in advance and is not deterred by setbacks. Bin Ladin associates surveilled the Embassies in Nairobi and Dar es Salaam as early as 1993, and some members of the Nairobi cell planning the bombings were arrested and deported in 1997.”
– CIA, “Terrorism: Bin Ladin Determined to Strike in the US,” (Senior Executive Intelligence Brief), The Central Intelligence Agency’s 9/11 File:, The National Security Archive, Aug. 7, 2001