The military judge in the September 11, 2001, attacks trial has ordered the US government to hand over correspondence on Guantanamo prison conditions and lifted restrictions on lawyers' communications with detainees.
The judge, Colonel James Pohl, will review years of reports by the International Committee of the Red Cross, the only human rights group to have access the US naval base in Cuba since it opened in 2002, according to one of two rulings revealed by defence lawyers.
After reviewing the massive collection of files, Pohl will decide whether the prosecution or lawyers representing the September 11 defendants can access them.
Although the ICRC has opposed releasing its confidential records to defence lawyers or the public, its correspondence is "the only independent historical record of the prisoners' time at Guantanamo", said James Connell, attorney for accused 9/11 co-conspirator Ali Abd al-Aziz Ali, also known as Ammar al-Baluchi.
He said the ICRC communication "may provide important information about the extremely harsh conditions of confinement at Guantanamo over the years".
In a separate ruling, Pohl for the first time allowed defence lawyers to communicate by mail with the five 9/11 suspects they represent on any topic relating to the case.
"For more than two years, I have not been able to communicate confidentially by letter, telephone or email with my clients at Guantanamo," Lieutenant-Colonel Sterling Thomas, who represents Ali, said.
"This new order opens the door to a more meaningful attorney-client relationship."
Lawyers representing the men accused of plotting the 2001 attacks that killed nearly 3,000 people on US soil have often pressed the US government to lift restrictions on communications with their clients.
They have protested against mail seizures, surveillance of their correspondence on a secure network and the presence of microphones hidden in smoke detectors in spaces where they met with their clients.
Prison authorities seized all legal mail from "high-value detainees" in October 2011 as part of a review.
Defence attorneys were later barred from using the Guantanamo legal mail system for privileged communications.
Following Pohl's ruling, the judge, not prison guards, will be in charge of controlling mail in a move praised by the defence.
"The issue of privileged legal communications has dogged the military commissions," Connell said.
Defence attorneys have argued that their inability to communicate confidentially with their clients when away from Guantanamo meant that they lacked a full attorney-client relationship.
"The new ruling implicitly suggests that the prior legal mail regime interfered with the attorney-client relationship, and needed to be changed," the lawyers said in a statement.