Testifying before the commission investigating the Sept. 11 attacks, the agent, Jose E. Melendez-Perez, who in a separate encounter barred an alleged al-Qaida operative from entering the country, said Atta was trying to use the wrong kind of student visa at Miami International Airport and should have been turned back.
Melendez-Perez said that Atta should have raised other red flags as well.
Atta was trying to switch his student visa to a tourist visa at the Miami airport - an unusual move that generally must be handled before a passenger leaves his or her country. Atta's appearance, he said, was also suspicious. He was older and traveling alone, and was too well-dressed to be coming to the country as a student.
"I would have recommended refusal," Melendez-Perez said.
The details surrounding Atta's entry were among a series of new facts to emerge yesterday that appear contrary to top administration officials' assertions last year that the 19 hijackers were "clean" and entered the country lawfully.
Commission investigators, for example, found that a number of hijackers used passports that had been partially forged and carried visas that might have been obtained fraudulently.
Of the four passports that were recovered after the attacks, two were "clearly doctored," investigators said, and they suspect at least six others presented at the border contained al-Qaida forgery.
While the specifics are classified, officials said people trying to enter the country without raising any alarms will change their names slightly, alter their places of birth or forge entry stamps to make it appear they have traveled extensively and without problems to countries that are allies of the United States.
Investigators also found that two other passports, those of hijackers Khalid al Mihdhar and Salem al Hazmi, were "suspicious" in other ways and could have been linked to al-Qaida, but they did not elaborate.
Investigators said they now believe from interviews and intelligence sources that three other hijackers - Nawaf al Hazmi, Ahmed al Nami and Ahmad al Haznawi - had the same suspicious indicators on their passports, though those passports were destroyed in the attacks.
In a prepared report, investigators also questioned how three hijackers who submitted visa applications with false statements were granted visas when the lies - such as whether they had applied for a visa in the past - could have been easily detected.
Investigators also found that hijackers Marwan al-Shehhi and Saeed al Ghamdi caused border agents to take a second look. Atta and al-Shehhi had been living in the United States and were returning from a short stay abroad. All three told immigration officials stories at variance with the visas they were carrying, but were allowed in anyway, the report said.
"The circumstances offered opportunities to intelligence and law enforcement officials," the report says. "But our government did not fully exploit al-Qaida's travel vulnerabilities."
The hearing was the first of two that wrap up today focusing on border and aviation security before the attacks. The commission, an independent, bipartisan panel, was created by Congress and President Bush to investigate the circumstances of the attacks and to make recommendations to prevent a recurrence. Its report is due May 27, but several panel members want the deadline extended.
Yesterday top immigration and State Department officials defended their efforts at stopping terrorists from entering the country. But, they said, the focus of the entry system at the time was on preventing illegal immigration.
Mary A. Ryan, former assistant secretary of state for consular affairs, who ran the department's visa program, said her agency was not included in watch lists from intelligence agencies that could have alerted it to possible terrorists.
Commission members pointed to the experience at Orlando International Airport of Melendez-Perez, who might have stopped a terrorist with just such an interview, an incident reported last week by the Orlando Sentinel, the Associated Press and USA Today.
Melendez-Perez received applause from the commissioners and spectators as he described how on Aug. 4, 2001, he refused to allow Mohamed al-Qahtani, whom some commission members described as the probable 20th Sept. 11 hijacker, to enter through the Orlando airport based almost entirely on a gut feeling the man was lying.
"I felt a bone-chilling, cold effect," he said. "He gave me the chills."
Melendez-Perez, who has been a border agent since 1992, said he met with al-Qahtani after the first agent to interview him referred him for a second round of questioning. From the beginning, he said, al-Qahtani's story had problems, and his hostility and arrogance didn't help him.
Melendez-Perez told commissioners he thought the man had military training because of his "impeccable" physical condition, his body language and a feeling that the man had knowledge of interview techniques. Al-Qahtani had only a one-way ticket from Dubai, no hotel reservations and insufficient money for the six-night stay he said he was planning.
At one point, Melendez-Perez said, al-Qahtani said someone was waiting for him upstairs. When pressed for the man's name and phone number, al-Qahtani told Melendez-Perez it was none of his business.
In fact, intelligence officials and commission investigators now believe that man was Atta, who used a pay phone that day at the airport to call a phone number investigators say was a known al-Qaida number.
Melendez-Perez said his co-workers told him he would get in trouble because al-Qahtani was a Saudi and it was an unspoken rule that Saudis were "to be treated with more tact" and rarely turned away. But he put him on a plane back to Dubai anyway.
After the attacks, Melendez-Perez said he told a fellow border agent to contact the FBI. He still has not spoken with the bureau, he said.
FBI spokesman Ed Cogswell said the FBI was alerted to al-Qahtani and the Orlando incident in July 2002 and is still trying to determine its significance.
Several months after al-Qahtani was turned back, he was picked up on the battlefield in Afghanistan, intelligence officials say, and is being detained in Guantanamo Bay, Cuba. "He wasn't on anybody's radar screen back then," Cogswell said. "But neither was Atta."