Insurance companies saw anomalous trading activities as well. Citigroup Inc. , which has estimated that its Travelers Insurance unit may pay $500 million in claims from the World Trade Center attack, had about 45 times the normal volume during three trading days before the attack for options that profit, if the stock falls below $40. Citigroup shares fell $ in late trading to $. Morgan Stanley , which occupied 22 floors at the World Trade Center, experienced bigger-than-normal pre-attack trading of options that profited when stock prices fell. Other companies directly affected by the tragedy had similar jumps. 
Bin Laden provided leadership and financial support for the plot, and was involved in selecting participants.  Bin Laden initially selected Nawaf al-Hazmi and Khalid al-Mihdhar , both experienced jihadists who had fought in Bosnia . Hazmi and Mihdhar arrived in the United States in mid-January 2000. In spring 2000, Hazmi and Mihdhar took flying lessons in San Diego, California , but both spoke little English, performed poorly with flying lessons, and eventually served as secondary – or "muscle" – hijackers.