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 a new diagnosis. The lesion, he said in an interview this week, "was consistent with cutaneous anthrax."
Dr. Tsonas's assertion, first made to the F.B.I. in October but never disclosed, has added another layer of mystery to the investigation of last fall's deadly anthrax attacks, which has yet to focus on a specific suspect.
The possibility of a connection between the Sept. 11 attacks and the subsequent anthrax-laced letters has been explored by officials since the first anthrax cases emerged in October. But a recent memorandum, prepared by experts at the Johns Hopkins Center for Civilian Biodefense Strategies, and circulated among top government officials, has renewed a debate about the evidence.
The group, which interviewed Dr. Tsonas, concluded that the diagnosis of cutaneous anthrax, which causes skin lesions, was "the most probable and coherent interpretation of the data available." The memorandum added, "Such a conclusion of course raises the possibility that the hijackers were handling anthrax and were the perpetrators of the anthrax letter attacks."
A senior intelligence official, who spoke on the condition of anonymity, said that George J. Tenet, the director of central intelligence, had recently read the Hopkins memorandum and that the issue has been examined by both the C.I.A. and the Federal Bureau of Investigation.
"No one is dismissing this," the official said. "We received the memo and are working with the bureau to insure that it continues to be pursued."
In their public comments, federal officials have said they are focusing largely on the possibility that the anthrax attacks were the work of a domestic perpetrator. They have hunted for suspects among scientists and others who work at laboratories that handle germs.
The disclosure about Mr. Alhaznawi, who died on United Airlines Flight 93, which crashed in Pennsylvania, sheds light on another front in the investigation. Senior law enforcement officials said that in addition to interviewing Dr. Tsonas in October and again in November, they thoroughly explored any connection between the hijackers and anthrax. They said the F.B.I. scoured the cars, apartments and personal effects of the hijackers for evidence of the germ, but found none.
Dr. Tsonas's comments add to a tantalizing array of circumstantial evidence. Some of the hijackers, including Mr. Alhaznawi, lived and attended flight school near American Media Inc. in Boca Raton, Fla., where the first victim of the anthrax attacks worked. Some of the hijackers also rented apartments from a real estate agent who was the wife of an editor of The Sun, a publication of American Media.
In addition, in October, a pharmacist in Delray Beach, Fla., said he had told the F.B.I. that two of the hijackers, Mohamad Atta and Marwan al-Shehhi, came into the pharmacy looking for something to treat irritations on Mr. Atta's hands.
If the hijackers did have anthrax, they would probably have needed an accomplice to mail the tainted letters, bioterrorism experts knowledgeable about the case said. The four recovered anthrax letters were postmarked on Sept. 18 and Oct. 9 in Trenton. It is also possible, experts added, that if the hijackers had come into contact with anthrax, it was entirely separate from the supply used by the letter sender.
For his part, Dr. Tsonas said he believed that the hijackers probably did have anthrax.
"What were they doing looking at crop-dusters?" he asked, echoing experts' fears that the hijackers may have wanted to spread lethal germs. "There are too many coincidences."
In recent interviews, Dr. Tsonas, an emergency room doctor, said Mr. Alhaznawi came into the hospital one evening in June 2001, along with a man who federal investigators believe was another hijacker, Ziad al-Jarrah, believed to have taken over the controls of United Flight 93.
They used their own names, he added, not aliases.
"They were well-dressed foreigners," he said. "I assumed they were tourists."
The men explained that Mr. Alhaznawi had developed the ulcer after hitting his leg on a suitcase two months earlier. Dr. Tsonas recalled that Mr. Alhaznawi appeared to be in good health, and that he denied having an illness like diabetes that might predispose him to such lesions. The wound, he recalled, was a little less than an inch wide and blackish, its edges raised and red.
Dr. Tsonas said he removed the dry scab over the wound, cleansed it and prescribed Keflex, an antibiotic that is widely used to combat bacterial infections but is not specifically recommended for anthrax.
The encounter lasted perhaps 10 minutes, Dr. Tsonas said.
He took no cultures and had no thoughts of anthrax, a disease at that time was extremely rare in the United States and was unfamiliar even to most doctors.
In October, amid news reports about the first anthrax victims, Dr. Tsonas, like other doctors, threw himself into learning more about the disease. An incentive was that his hospital is relatively near American Media, so victims there might come to Holy Cross for treatment.
Dr. Tsonas said he forgot entirely about the two men until federal agents in October showed him pictures of Mr. Alhaznawi and Mr. Jarrah, and he made positive identifications.
Then, agents gave Dr. Tsonas a copy of his own notes from the emergency room visit and he read them. "I said, `Oh, my God, my written description is consistent with cutaneous anthrax,' " Dr. Tsonas recalled. "I was surprised."
He discussed the disease and its symptoms with the agents, explaining what else could possibly explain the leg wound. A spider bite was unlikely, he said. As for the hijacker's explanation — a suitcase bump — he also judged that unlikely.
"That's a little unusual for a healthy guy, but not impossible," he said.
After his meetings with F.B.I., Dr. Tsonas was contacted early this year by a senior federal medical expert, who asked him detailed questions about the tentative diagnosis.
Last month, experts at Johns Hopkins also called Dr. Tsonas, saying they, too, were studying the evidence. The Hopkins analysis was done by Dr. Thomas Inglesby and Dr. Tara O'Toole, director of the center in Baltimore and an assistant secretary for health and safety at the federal Energy Department from 1993 to 1997.
In an interview, Dr. O'Toole said that after consulting with additional medical experts on the Alhaznawi case, she was "more persuaded than ever" that the diagnosis of cutaneous anthrax was correct.
She said the Florida mystery, as well as the entire anthrax inquiry, might benefit from a wider vetting.
"This is a unique investigation that has many highly technical aspects," she said. "There's legitimate concern that the F.B.I. may not have access to the kinds of expertise that could be essential in putting all these pieces together."
John E. Collingwood, an F.B.I. spokesman, said the possibility of a connection between the hijackers and the anthrax attacks had been deeply explored.
"This was fully investigated and widely vetted among multiple agencies several months ago," Mr. Collingwood said. "Exhaustive testing did not support that anthrax was present anywhere the hijackers had been. While we always welcome new information, nothing new has in fact developed."