The amount of U.S. currency circulating outside banks rose sharply in July/August 2001. The growth ran into the billions of dollars, and was concentrated in $100 bills. These large-scale currency movements matter for anyone who cares about learning the truth about 9/11.
Under money laundering and other laws, assets can be frozen and seized in the banking system. Knowing this, parties concerned that their assets might be frozen or otherwise at risk after 9/11 would have had an incentive to liquidate securities and banking accounts beforehand, and withdraw their money in difficult-to-trace ways. This could have happened in U.S. banking and securities accounts, as well as accounts denominated in U.S. dollars outside the United States. Finding the parties responsible for large-scale withdrawals of currency before 9/11 could help identify people aware of, if not responsible for, those events.