starting early wednesday morning , the tenth day of november , twelve detectives began surveillance of the check-in counters at continental , delta , us airways , american , northwest , and united airlines , looking for a jamaican with a knife scar who might be headed for either houston-intercontinental or houston-hobby on a direct flight , or on any one of the flights connecting through charlotte , dallas/fort worth , new orleans , detroit , chicago , memphis , atlanta , cleveland , pittsburgh , or philadelphia .