US Secretary of State Colin Powell's announcement that federal investigators were preparing to outline America's case against Osama bin Laden (pictured) to allies and the public is only the most recent sign that the Bush administration is confident its inquiry has uncovered substantial evidence linking the attacks to the Saudi fugitive.

While much of this evidence is secret - Mr Powell on Monday said that a significant portion of the information gathered for the report would remain classified - interviews with law enforcement officials and published reports show the two-week inquiry has already found a number of ties between the hijackers and Mr bin Laden.

The most promising break appears to be the arrest last week near Chicago of Nabil al-Marabh, a 34-year-old Kuwaiti who is believed to have close ties to two hijackers and Mr bin Laden's Al-Qaeda organisation.

Federal authorities believe that Mr al-Marabh had financial dealings with Satam al-Suqami and Ahmed Alghamdi, hijackers on the two Los Angeles-bound aircraft that crashed into the World Trade Center. In addition, Raed Hijazi, a Palestinian who worked for the same Boston taxi company as Mr al-Marabh, has told Jordanian authorities that Mr al-Marabh was a bin Laden operative.

Mr Hijazi, 32, has reason to know: he is being held in Jordan for plotting terrorist attacks against American targets in the Middle East during millennium celebrations, a plot Jordanian intelligence officers believe was supported by Al-Qaeda. He is also alleged to have trained in Al-Qaeda camps in Afghanistan.

Even more intriguing to investigators is Zacarias Moussaoui, a 33-year-old French Algerian whom some authorities suspect of being the fifth hijacker on the aircraft that crashed in Pennsylvania. The United Airlines flight was the only one with four hijackers aboard; the others had five.

Mr Moussaoui took classes at pilot schools in Oklahoma and in Minnesota, where instructors - suspicious that a man with limited flying experience was trying to pay cash to learn how to pilot large commercial jetliners - turned him into the FBI.

Soon after he was arrested on immigration charges in August, French intelligence told US counter-terrorist agents that Mr Moussaoui was a Muslim extremist who may have trained at Afghan camps tied to Mr bin Laden. Mr Moussaoui has been arrested as a material witness and was flown to New York for questioning.

Even before the attacks on September 11, two of the hijackers were on an FBI watch list for their connections with Mr bin Laden. Khalid al-Midhar and Nawaf Alhamzi, both on the American Airlines flight that crashed into the Pentagon, were videotaped in 1999 in Malaysia meeting two Al-Qaeda lieutenants who have been tied to the bombing last year of the USS Cole in Yemen.

The CIA informed the FBI and immigration authorities of the connection on August 23, but immigration records showed the men had already entered the US by then. An FBI search proved fruitless.

A separate and potentially more critical link to Mr bin Laden's organisation is being investigated in Germany, where Mohammed Atta, a 33-year-old Egyptian who authorities suspect might have been the leader of the 19 hijackers, lived before moving to the US.

Mr Atta has direct ties to five other hijackers - more than any of the other terrorists - including Marwan al-Shehhi, a 23-year-old from the United Arab Emirates, and Ziad Jarrah, a 26-year-old Lebanese national, both of whom attended a technical university with Mr Atta in Hamburg.

German authorities have issued arrest warrants for two other fellow students of Mr Atta who are believed to helped plan the attack. Although Kay Nehm, Germany's chief federal prosecutor, has said there is no evidence yet linking the Ham burg cell to Mr bin Laden, Reinhard Wagner, the head of the Hamburg office of Germany's domestic intelligence service, has said there is a broad network of bin Laden supporters in the city.

Despite the breaks in the investigation, much publicly available evidence linking Mr bin Laden to the attacks remained circumstantial, terrorism experts said.

Additional reporting by Hugh Williamson in Berlin