One of the alleged September 11 plotters protested angrily in court and defied a judge Thursday over searches of his cell at the Guantanamo Bay prison and the seizure of confidential files.

Walid bin Attash's outburst came on the last day of a round of pretrial hearings for five suspects who face the death penalty if convicted over the 2001 hijacked plane attacks on the United States. Nearly 3,000 people died.

"In the name of God, there is an important thing for you," the heavily bearded man said as he stood up to complain and address the court.

But the military judge, Colonel James Pohl, cut him off several times and ordered him to sit down.

Bin Attash, wearing a large white robe, finally took a seat after about 10 minutes when his legal team managed to calm him down. A Yemeni native who grew up in Saudi Arabia, he stands accused of providing logistical support to the 9/11 hijackers.

Defense lawyer Cheryl Bormann said bin Attash was "very upset" because guards had searched his cell during a court hearing, and seized documents containing communications with his attorneys about the case.

Bin Attash now fears that every time he comes to court, his legal papers will be seized, she added.

Lawyers said the cells of four of the suspects had been searched. In addition to bin Attash, guards also seized the legal correspondence of the self-proclaimed mastermind of the attacks, Khalid Sheikh Mohammed, and Yemen's Ramzi Binalshibh.

But a prison camp lawyer defended the searches as "routine inspections," saying guards had been concerned because some of the items were missing security stamps, and others were not all identical as the markings had apparently changed over the years.

"The materials contained in them were disturbing" to the guards, Lieutenant Commander George Massucco said.

In addition to the legal documents, guards seized a copy of the US government's "9/11 Commission Report" on the attacks, a photo of Mecca and toilet paper with notes scribbled in English.

Chief Prosecutor Brigadier General Mark Martins promised an investigation into the alleged seizures. Despite the lawyers' protests, the judge ordered that the hearings continue.

At the end of the hearing, prosecutor Ed Ryan proposed to remove concealed microphones disguised as smoke detectors in rooms where the defendants meet with their lawyers, amid protests by the defense lawyers over strict surveillance of their exchanges with their clients.

"The sooner, the better," Pohl said.

The five defendants are being tried by a military commission, a tribunal for war crimes. The next set of hearings is due April 22-26 but the trial is not expected for more than a year at the earliest.

The hearings at the US naval base and prison in Cuba for terror suspects are being broadcast by video link to the Fort Meade military base outside Washington.