GUANTANAMO BAY NAVAL BASE – A photo of the World Trade Center in flames was found in the possession of the self-proclaimed mastermind of the September 11 attacks at Guantanamo Bay detention center, a military court heard on Thursday.

On the third day of a pre-trial hearing regarding five "high-value" detainees accused of involvement in the attacks, the court heard that the prisoners' possessions were the subject of regular searches.

Navy Commander George Massucco admitted under questioning that "several searches" carried out since February included monitoring of "privileged" correspondence between the five defendants and their lawyers.

Attorneys for the five men, who face the death penalty if they are eventually tried and convicted for the murders of nearly 3,000 people on September 11, 2001, have protested against the seizure of confidential documents marked as legal papers and their subsequent disappearance.

But Massucco insisted the team in charge of the searches at Guantanamo's Camp 7, known as "Task Force Platinum", had only looked for items deemed to be "contraband in nature" and was not interested in the contents of legal correspondence.

Cells were searched to maintain "the safety of the guardforce," Massucco said, stating that staples, paperclips, metal items and zip ties were the sorts of items officers searched for.

The photo of the World Trade Center on flames was found in the possession of 9/11 mastermind Khalid Sheikh Mohammed, Massucco added under questioning from a prosecutor.

Arabic newspapers and 87 pages of articles from the website GitmoWatch had also been found in Mohammed's cell, he added.

Defense attorney Walter Ruiz meanwhile said a list of items marked "defense strategy" had been taken and were being held by an "evidence custodian" at the base.