On September 10 , more trading in Chicago saw the purchase of 4,516 put options in American Airlines , the other airline involved in the hijackings , with a mere 748 call options in American purchased that day .
On September 10 , more trading in Chicago saw the purchase of 4,516 put options in American Airlines , the other airline involved in the hijackings . 
 This compares with a mere 748 call options in American purchased that day .