That site is full of confused, misleading and contradictory information apparently designed to mislead people. In few fields of 9/11 skepticism does that site get it more wrong than on the suspicious financial transactions leading up to 9/11.
Worst of all is that site's citation of the 9/11 Commission Report's conclusion about the transactions appears to be deliberately misleading.
The most misleading ploy used by defenders of the "official story" is the framing of the question. You asked the appropriate question -- about suspicious trading. The cite you were referred to tries to narrow this down to a false question -- did the terrorists themselves trade on American and United airline stock -- a question, that no one would ever be able to answer even if the answer were affirmative.
The underlying question isn't whether the terrorists or co-conspirators traded on airline stock; the question is
whether there was foreknowledge of a terrorist event in general that made its way to the financial markets. If there was, then the secondary question is, if actors in the financial markets knew about it, why didn't the federal authorities know about.
Moreover, when financial markets "know" about an event, it doesn't mean that the particular traders are involved in the event or even know specifically what is going to happen. That's why the Pentagon's DARPA wanted to create a "terrorism futures market" -- because markets have a way of sniffing out information, even if it is second or third hand.
So just before 9/11, there was not a specific terrorist engaged in suspicious trading activity; there was lots of trading activity that indicated foreknowledge had made its way to several financial markets. This is why the 9/11 Commission's dismissal of the issue was so idiotic. In a footnote, the 9/11 Commission reduces all that activity to a single trade by a single institutional investor and finds nothing and says therefore there was no suspicious activity in the financial markets.
The suspicious activity took many forms. One form was the purchase of put options on airline stock. The official story propoganda site you were referred to confusingly introduces paragraphs from the Poteshman study taken out of context to suggest that Poteshman concluded that terrorists were not trading on airline stock. But it buries Poteshman's actual conclusion:
Consequently, the paper concludes that there is evidence of unusual option market activity in the days leading up to September 11 that is consistent with investors trading on advance knowledge of the attacks.
That is the takeaway from the Poteshman study.
That, however, was only one kind of suspicious activity. There was also insider trading, and the insider trading story has more confusing links to 9/11 and federal authorities. To summarize a complicated story, there was an American-based Egyptian financier, named Tony Elgindy, who specialized in short selling and who published a short selling newsletter. Elgindy had been involved in jihadist activities in Kosovo earlier in his life. Elgindy also, however, was an FBI informant and was working with a "rogue" FBI agent who developed an elaborate scheme to "punish" companies he was investigating by having Elgindy's newsletter publish bad news about the company. Elgindy and the rogoue agent also traded on advance knowledge of what Elgindy would publish.
Elgindy recommended to his readers the weekend before 9/11 that a catastrophic event was going to occur that would cause the markets to plummet. Elgindy himself tried to liquidate much of his portfolio immediately before 9/11 -- on the morning of 9/10.
Eventually Elgindy and the rogue FBI agent were prosecuted for insider trading and in open court, the US attorney alleged that Elgindy had foreknowledge of the 9/11 attacks.
You can read about this here:
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=125x195924#196210and here:
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=125x195974#196097There was also evidence of massive trading in Europe, but I'll leave it to someone with more expertise in that area to fill you in.
So, as you can see it's a complicated story of widespread foreknowledge that was indicated by a multitude of moves in the financial markets. Please don't fall for the "official conspiracy theory" apologists who try to simplify and obfuscate this imortant story.
On edit: Here is a link to the suspicious financial activity in Europe. The first entry on this page explains that it was trading in reinsurance companies:
http://www.historycommons.org/context.jsp?item=a0901reinsurance