FORT MEADE, Md - U.S. military prosecutors and defence lawyers argued Monday over evidence against an Army intelligence analyst charged with leaking massive amounts of secret U.S. data to WikiLeaks, while the public was shut out as the hearing dealt with classified but widely publicized information.

The hearing, in its fourth day, is to determine whether Pfc. Bradley Manning should be court-martialed on 22 charges, including aiding the enemy. If convicted, the 24-year-old could face life in prison.

The government was expected to call up to eight more witnesses to testify. The defence would then present its case.

In the most potentially damaging evidence so far, an investigator said Sunday he found more than 10,000 downloaded diplomatic cables and other sensitive information on a computer Manning used.

But pressed under cross-examination, David Shaver said some of the cables didn't match any of those published by WikiLeaks. The damaged file could only be opened with special tools, which could explain why those documents weren't released, he said.

Defence attorneys argue the leaked material did little or no damage to U.S. interests. They have neither acknowledged nor denied that the intelligence analyst was behind the leaks.

But a decision by presiding officer Paul Almanza to remove spectators and reporters for a half-hour of the hearing Monday morning was a worrying sign for Manning's defence.

By ruling the diplomatic and military information in question should somehow remain secret, even though it has been published by media around the world, Almanza effectively undermined the defence argument that no harm was done and the information might as well be public.

Manning's supporters fumed. The defence already has appealed for Almanza to be removed from the case because of his civilian job with the Justice Department, which is conducting a separate investigation of WikiLeaks chief Julian Assange.

Almanza "is seeking to prevent journalists and the public from reporting on testimony related to materials that are already in the public domain," said a group called the Bradley Manning Support Network.

A member of the group, Daniel Choi, was ejected from the area Monday. Choi had been cleared through security and was seen standing outside in a group that included Pentagon Papers leaker Daniel Ellsburg, presumably to attend court. But Choi was taken back into a security trailer, where he remained with military police for at least 10 minutes before he was escorted away. A security official would say only that Choi had done something he'd been asked not to do.

Shaver's testimony Sunday illustrated how the government connected the dots in its case accusing Manning of committing traitorous leaks from his perch as an intelligence analyst in Baghdad.

He told the hearing that in addition to thousands of State Department cables, he found several versions of a deadly 2007 helicopter attack video and secret assessments of terrorist detainees at Guantanamo Bay, Cuba. He also said he discovered evidence that someone had used the computer to streamline the downloading of cables with the apparent aim of "moving them out."

All the material was linked to the username "bradley.manning" or Manning's user profile, Shaver said.

The other computer was used to conduct scores of online searches for the anti-secrecy website WikiLeaks and its founder, Assange, he said.

Manning has remained calm during the hearing. He hasn't spoken in the last three days, except for the few occasions he has leaned over to consult with his civilian attorney, David Coombs.

Manning's defence has challenged the government to explain why a private said to have upended furniture in fits of rage and exhibited a pattern of troubled behaviour was allowed to keep working with highly sensitive information.

After Almanza's recommendation, the Army says it may take several weeks for the commander of the Military District of Washington to decide whether Manning will be court-martialed.

Maj. Gen. Michael Linnington may choose other courses, including administrative punishment or dismissal of some or all counts. He also could add more charges based on evidence produced at the hearing.