Federal authorities have made more arrests in a widening investigation into an Idaho-based group suspected of using the Internet to promote and finance an organization that supports terrorism.

Abdullah al-Kidd, a U.S. native and a former University of Idaho football player, was arrested Sunday at Dulles International Airport en route to Saudi Arabia. He is being returned to Idaho as a material witness in the probe, law enforcement officials said.

Authorities have arrested three other men in the Idaho probe in recent weeks. The FBI is examining links between the Idaho men and purported charities and individuals in six other jurisdictions across the country.

A central figure in the probe, Sami Omar al-Hussayen, a Saudi doctoral student in computer science at the University of Idaho, was indicted last month for allegedly lying on immigration forms about his activities in the United States. The government contends al-Hussayen financed and administered Web sites for the Islamic Assembly of North America, a Michigan-based group that the government said has published material advocating suicide attacks on the United States.

Authorities said al-Kidd was taken into custody because his name was on a Customs watch list. The FBI has been seeking to interview him about payments of about $20,000 he allegedly received from al-Hussayen and his associates. Authorities also want to know about a trip to Yemen al-Kidd made in August 2001, returning to the United States in April 2002.

Al-Kidd, who authorities say converted to Islam in 2000, has previously told reporters that he went to Yemen to study Islamic law and learn Arabic.

In recent days, authorities disclosed that another man arrested this year on bank fraud charges is connected to the case through his association with al-Hussayen. Former University of Idaho student Bassem K. Khafagi is facing charges in Michigan. Khafagi, an Egyptian, received a master's degree in engineering from the university.

A fourth man, Ismail Diab, was arrested as a material witness March 1 in a related case in Syracuse, N.Y. Four men there are charged with transferring funds illegally to individuals in Baghdad using a charitable organization called Help the Needy, an offshoot of the Islamic Assembly of North America. Diab previously lived in Pullman, Wash., a few miles from the University of Idaho.

At a detention hearing last week, al-Hussayen's brother and his faculty adviser said that they had never known him to advocate terrorism and that he should not be considered a flight risk because he is committed to getting a degree. A federal magistrate ordered his release on the criminal charges, but he remains in the custody of immigration officials.

Abdullah al-Kidd, in an undated photo, is being held as a material witness in the investigation.