he two men identified themselves as pilots when they came to the emergency room of Holy Cross Hospital in Fort Lauderdale, Fla., last June. One had an ugly, dark lesion on his leg that he said he developed after bumping into a suitcase two months earlier. Dr. Christos Tsonas thought the injury was curious, but he cleaned it, prescribed an antibiotic for infection and sent the men away with hardly another thought.But after Sept. 11, when federal investigators found the medicine among the possessions of one of the hijackers, Ahmed Alhaznawi, Dr. Tsonas reviewed the case and arrived at...