The September 11 hijackers probably used gas or spray such as mace against passengers and crew on the first plane to hit the World Trade Centre, an FBI agent told a German court yesterday.

FBI special agent Matthew Walsh, giving evidence at the trial of Mounir El Motassadeq, the first suspected conspirator to stand trial, said a stewardess on board had said in a telephone conversation that she was having trouble breathing.

Walsh told the court in Hamburg, the American Airlines stewardess said a number of people had been stabbed. He continued: "She also stated it was very hard to breathe, so we assume that mace or another gas was used."

Mace is an irritant spray commonly used to ward off assailants.

Official US reports on the attacks have been sparing on detail and Walsh's remarks appeared to shed some new light on what happened.

In cautious testimony, he told the court the stewardess called in details of the hijack shortly before the crash, the first of four that killed a total of about 3,000 people.

"On the telephone she said she saw these people stabbing a passenger as well as other flight crew," he said. "The passenger in 10B had stabbed the passenger in front of him. She thought the passenger was already dead.

"I believe he had his throat cut," he said. Walsh, 33, gave a broad overview of the vast US investigation into the attacks for the trial of Motassadeq.

Despite the efforts of thousands of officials, elements leading up to the attacks still puzzled investigators, including two visits to Las Vegas by plot leader Mohamed Atta.

"As far as Las Vegas goes, we're not sure," Walsh said. "We don't know what they were doing every day at each of these locations."

Atta, the ringleader, and two other pilots lived in the port city of Hamburg during the 1990s. Moroccan student Motassadeq is charged with serving as the paymaster of the al Qaeda cell based in Hamburg which is accused of masterminding the attacks.

Walsh told the court that the pilot of the second plane which crashed into the World Trade Centre, Marwan Al Shehhi, received more than $10,000 in transfers from Ramzi bin al-Shaibah, a former Hamburg resident accused of playing a major role and who is in US custody.

Washington has barred bin al-Shaibah, known in the West as Binalshibh, from testifying in the Hamburg case, prompting Motassadeq to ask Walsh. "I have one question: can you tell me why Ramzi bin al-Shaibah should not testify?" the defendant asked in accented German.

"That is beyond the scope of what I am allowed to talk about," Walsh replied in English.

Walsh told the court of an extensive law enforcement effort. The FBI contacted every flight school in the United States and researched all passengers on the plane to seek common links.

"On the whole all the hijackers as (flight) students were reserved and kept to themselves," he said. "They were not widely known, at least these four, as being good pilots."

After gaining pilot licences, they trained on a flight simulator, Walsh said. "Instructors who taught those sessions said they were only interested in turns and approaches."

During the testimony, Motassadeq mostly listened quietly, taking some notes.

Walsh told the court the plotters had funds left over after training, even after Atta and two others visited Las Vegas a few weeks before the attacks.

"In the days leading up to September 11 it seems that the hijackers were returning the money they no longer needed," Walsh said of a wire transfer to the United Arab Emirates.

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