(Updates with comments from prosecutor, Mohammed's lawyer)
By Jane Sutton
GUANTANAMO BAY U.S. NAVAL BASE, Cuba, Sept 18 (Reuters) - M onths of efforts to fix a file-gobbling computer system used by defense lawyers in the Guantanamo war crimes tribunal have only turned up more problems, the chief defense counsel testified on Wednesday.
Defense lawyers asked the U.S. military judge to halt pre-trial hearings in the death penalty case against five alleged conspirators in the Sept. 11 plot until the technical problems are fixed, which is not expected to happen before early next year.
Files began vanishing in January and the chief defense counsel, Air Force Colonel Karen Mayberry, ordered defense lawyers to stop putting confidential documents on their computer network in April because the data breaches had shown the system was not secure.
"We've got more issues now than we did then," Mayberry testified in the top-security courtroom at the Guantanamo Bay U.S. Naval Base.
The defendants include the alleged mastermind of the hijacked plane attacks that killed nearly 3,000 people on Sept. 11, 2001, Khalid Sheikh Mohammed. He and four co-defendants could be executed if convicted of conspiring with al Qaeda, terrorism and murder.
Only two of them, Yemeni captives Ramzi Binalshibh and Walid bin Attash, came to Wednesday's session. Binalshibh was ejected from court for disruptive behavior earlier in the week but sat quietly as Mayberry testified.
Massive amounts of data were lost when technicians tried to create a system that would simultaneously update files the lawyers worked on at Guantanamo and those on their computer network in the Washington area, she said.
Some documents vanished, others were replaced with older versions, and gaps in the backup system were revealed, Mayberry said.
One prosecutor was temporarily given access to some defense files, and new problems arose when technicians switched some Pentagon personnel to a new email system, she said.
"Folks were hitting 'send' and thinking that emails went through and they weren't," Mayberry testified.
Attachments were stripped off, emails from the judge's office were never received and phone callers began asking the lawyers why they had not replied to messages they had never seen, she said.
Exasperatingly, technicians asked her to compile a list of all the emails she had never gotten, she said.
As some files were restored, Mohammed's lawyers found changes had been made to some documents on days the lawyers never touched them, and hidden files had been attached to others.
One of them, David Nevin, suggested intelligence agencies were responsible for the breaches.
Defense lawyers said previously that they put draft documents on external hard drives, loaded them onto personal laptops and emailed them to colleagues using the public wi-fi at Washington-area Starbucks or at a coffee shop on the Guantanamo base.
Prosecutor Ed Ryan questioned whether that was safe, given frosty U.S. relations with Cuba.
"We happen to be on a foreign island whose government doesn't like us very much," Ryan said.
It was unclear whether the judge, Army Colonel James Pohl, would rule before the weeklong hearing ends on Friday. (Editing by Kevin Gray and Cynthia Osterman)