Proceedings are under way in the US state of Florida in the trial of a man once suspected by the US of plotting to detonate a "dirty bomb".
Jose Padilla was arrested at Chicago airport in May 2002
Jose Padilla, a US citizen, is accused of aiding Islamic extremists and conspiracy to murder US nationals overseas. He denies the charges.
Mr Padilla was held without charge in a US military jail for over three years.
The 36-year-old was arrested at Chicago's O'Hare Airport in May 2002 after he returned from Pakistan.
At that time, US officials said that they had thwarted an al-Qaeda plot to detonate a radioactive bomb in a major city, but these allegations have now been dropped.
Two other men - Adham Amin Hassoun and Kifah Wael Jayyousi - are being tried alongside Mr Padilla.
As jury selection got under way, Judge Marcia Cooke told prosecutors not to try to link the case to the 11 September 2001 attacks on New York and Washington.
But prosecutor John Shipley said that testimony would link the defendants with extremism.
"They certainly supported al-Qaeda, there's no question about that," he said.
Mr Padilla, a former Chicago gang member of Puerto Rican descent, is a convert to Islam.
The US government, which once branded him an "enemy combatant", says he provided money and recruits to Islamic extremists.
It also alleges he travelled overseas to train as a terrorist and aimed to carry out "violent jihad".
After his arrest in 2002, Mr Padilla was held at a US base in South Carolina where, he says, he was tortured. US officials deny that he was abused.
The BBC's Andy Gallacher in Miami says that the case is expected to set the stage for a fierce fight between civil liberties groups and the administration of US President George W Bush.
Mr Padilla could face life in prison if convicted.