Tracing the transactions would not be an issue, if by the time the investigators got around to trying to talk to the account holders, they would only discover the account holders did not exist or had disappeared, the addresses were abandoned buildings, and the money had already been wired overseas
Either that, or the people doing the trading were doing so in the arrogant belief that they could not be touched (like members of the Saudi Royal family)
It wasn't just those two airlines. Boeing saw large put volume (several million dollars worth), as well as insurance companies and other guys affected by the collapse of the WTC. Add up the millions, and you start talking about significant amounts of money. Maybe not by Federal Budget standards, but big money to non-governments