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Federal authorities say a U.S. student has admitted to plotting with Al Qaeda (search) to kill President Bush. But they also acknowledge that many of his statements were made without a lawyer present, raising questions about whether they will be admissible in court.

The government has yet to lay out its case fully against Ahmed Abu Ali (search), 23, a Virginia resident held in Saudi Arabia (search) for 20 months without charges. He was returned to the United States last week, where a federal indictment was unsealed charging him with conspiracy and providing material support to terrorists, including discussing ways to assassinate Bush.

Abu Ali's family and lawyers say he is innocent and claim he was tortured and threatened by the Saudis, making anything he might have said worthless in court. Some of his statements to his Saudi interrogators were videotaped, an FBI agent testified at a detention hearing this week.

"That's the $50,000 question in this case — the circumstances surrounding the interrogations, whether there were any threats and violence, whether confessions were voluntary in any way," said Edward MacMahon, a former lawyer for Abu Ali.

U.S. Attorney Paul McNulty of the Eastern District of Virginia said allegations of torture are an "utter fabrication."

Another federal law enforcement official, who spoke only on condition of anonymity because the criminal case is pending, said the government has not disclosed all its evidence.

In some past terrorism cases the Justice Department (search) initially has outlined grand schemes only to later have defendants convicted of relatively minor infractions such as document and credit card fraud and immigration violations.

In Detroit, the first post-Sept. 11 prosecution of an alleged terrorist sleeper cell collapsed amid evidence of prosecutorial misconduct, and the government is now pursuing insurance fraud charges against the men.

Still, administration officials have defended their approach, saying it is better to identify suspected terrorists and get them off the streets for minor crimes than wait for them to launch deadly plots.

Federal authorities have arrested 379 people on terrorism-related charges in the past year and obtained convictions in 200 cases, Attorney General Alberto Gonzales said in testimony to Congress this week.

In the Abu Ali case, questions center on how the government obtained evidence against him.

FBI agent Barry Cole testified at a detention hearing that Abu Ali admitted many times that he joined Al Qaeda and discussed various potential acts, including a plan in which he would personally assassinate Bush.

Cole said he interviewed Abu Ali over four days in September 2003. He said Abu Ali initially demanded a lawyer but changed his mind after agents told him he could be prosecuted by Saudi authorities or held as an enemy combatant. His family has described such talk as thinly veiled threats to scare Abu Ali into talking.

In a case with some similarities, a federal judge said statements made by Sabri Benkhala, a U.S. citizen, to federal agents were not voluntary and could not be used, said John Keats, Benkhala's lawyer. Benkhala was acquitted of supplying services to the Taliban and other charges stemming from his alleged role in what prosecutors called a "Virginia jihad network."

Prosecutors sought to link Abu Ali to the same group, but have not charged him with any role in it.

At a 2003 detention hearing for Benkhala, assistant U.S. Attorney David Laufman told U.S. District Judge Leonie Brinkema that Abu Ali was a member of a Saudi-based Al Qaeda cell and that he was told he needed to either organize a terrorist operation or return to the United States and establish an Al Qaeda cell.

That statement also was similar to what Cole testified to in court this week.

The government also has said one of two people Abu Ali talked to about assassinating the president was killed by Saudi authorities in 2003. Cole said Abu Ali's confessions are supported by the admissions of an Al Qaeda cell leader in Saudi Arabia who surrendered to authorities.