A US military judge at Guantanamo Bay temporarily suspended Tuesday the pre-trial hearing for the five alleged September 11 plotters after the defense said the FBI had investigated them.
Halting the hearings until at least Thursday, Judge James Pohl said he wanted to know to what extent the allegations were true.
On Monday, defense attorney Jim Harrington alleged that a "member of my team, visited by two members of the FBI, had to sign and answer" questions by Federal Bureau of Investigation agents.
David Nevin, representing the self-proclaimed mastermind of the 2001 attacks on US soil Khalid Sheikh Mohammed, told the hearing that the FBI investigation had a "chilling effect" on the defense team.
The delay to the proceedings -- which were relayed by video to a military base in Fort Meade -- centered on a personal document and two letters belonging to Mohammed that were smuggled out of the ultra-secure prison in Cuba.
One of the leaked pieces of material was a pamphlet entitled "The Road to Real Happiness" that was published in January by The Huffington Post and Britain's Channel 4.
Pohl said he wanted to know the full extent of alleged FBI investigations trying to determine how the materials belonging to Mohammed got out and if the defense was responsible.
Prosecutors accused the defense of seeking to delay the proceedings.
This week's hearings are paving the way for a full trial that is not expected to open before 2015.