Washington-Attorneys for Khalid Sheikh Mohammed, the suspect who has taken credit for masterminding the attacks on Sept. 11, 2001, have called on the judge and the entire prosecution team in Mohammed’s military commission at Guantanamo Bay to step down.

The attorneys have accused the judge, Army Col James Pohl, over what they called “at least the appearance of collusion” that led to the government apparently secretly destroying information relevant to the premier post-9/11 tribunal.

The accusation comes in a 10 May defense filing that the military commissions have recently unsealed. It contains significant detail about an episode that Mohammed’s attorneys say has permanently tainted the most high-profile test of the U.S.’s post-9/11 turn toward military justice for terrorism cases.

The defense team’s move could be a possible obstacle to the case of Pakistan-born Mohammed and four others who are accused of hijacking the planes to carry out the 9/11 attacks in the United States which left 3,000 people dead.

According to the defense filing, six months after Pohl issued an evidence-preservation order at the defense’s behest and over the prosecution’s objections, the judge “authorized the government to destroy the evidence in question.”

Pohl’s reversal of course was “the result of secret communications between the government and Judge Pohl, which he conducted without the knowledge of defense counsel,” the motion asserts.

That order, issued exclusively to the prosecution, carried with it a direction to provide the defense with a “redacted version.”

But Pohl “did not actually instruct the prosecution to proffer any proposed redactions of the order until 18 months after granting the government permission to destroy the evidence, and over a year after it was apparently actually destroyed,” the defense team claims.

The details of the court document were published by The Guardian newspaper.