In addition to the targets that were hit on Sept. 11, Mohammed initially proposed crashing hijacked planes into the CIA and FBI headquarters, unidentified nuclear power plants and the tallest buildings in California and Washington state," the report says.

"The centerpiece of his original proposal was the tenth plane, which he would have piloted himself," it says. Instead of crashing it in a suicide attack, Mohammed would have killed every adult male passenger on the plane, contacted the media from the air and landed the aircraft at a U.S. airport. Then he would have made a speech denouncing U.S. policies in the Middle East before releasing all the women and children, the report says.

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The final date was likely influenced in part by the targets chosen, investigators also found. An electronic communication between Atta and Binalshibh showed that Atta finally selected a date after the first week in September "so that the United States Congress would be in session."

Bin Laden strongly favored targeting the White House, and Binalshibh urged Atta to agree. But Atta was concerned that the presidential mansion was too difficult to hit, and backed the U.S. Capitol instead. The matter appears to have been unresolved as late as two days before the attack.