Some 110,000 classified cables were found on alleged Wikileaks source Bradley Manning's computer, day four of his pre-trial hearing has heard.
Digital investigator David Shaver acknowledged at the Fort Meade military base court there was little indication any of the files had been circulated.
But another computer expert testified that Manning had admitted leaking documents, during an online chat.
The hearing will determine if the 24-year-old should face a court-martial.
Charged with 22 counts of distributing state secrets, the former US Army intelligence analyst could face life in prison if convicted.
Mr Shaver told the hearing in the US state of Maryland on Monday that he had found 110,000 US state department cables on Pte Manning's workstation.
However, it was not clear if they had been shared, and some of them did not match any of the ones published by Wikileaks, he conceded.
About 10,000 of the documents were held in a corrupted file, possibly explaining why they were never published.
Another investigator, Mark Johnson, testified that he found records of internet chats with a former hacker on Pte Manning's computer, in which the defendant admitted leaking all the cables.
Pte Manning was arrested in May 2010 after the hacker handed records of this correspondence to the authorities.
Mr Shaver, a special agent with the Computer Crimes Investigative Unit, said that among the classified files on Pte Manning's computer were several versions of a helicopter attack video from 2007 and assessments of Guantanamo Bay detainees.
He also said he had found more than 100 internet searches on a workstation used by Pte Manning for "Wikileaks" and "Julian Assange" - founder of the anti-secrecy website.
The court was cleared of the media and general public on Monday for about half an hour, despite objections from the defence, so that Mr Shaver could testify about the classified material.
Supporters of Pte Manning, who have been demonstrating near the main entrance of the base, voiced outrage at the closed court session.
One organisation, the Bradley Manning Support Group, said the move was an attempt "to prevent journalists and the public from reporting on testimony related to materials that are already in the public domain".
Defence lawyers argue that the leaked material did little or no damage to US interests.
Pte Manning's legal team have also asked why his superiors did not suspend his security clearance despite his unpredictable behaviour, which included turning furniture over in a fit of rage.
A supervisor who was called to testify on Sunday invoked his Fifth Amendment right against self-incrimination and did not take the stand.
The hearing has also heard how Pte Manning struggled with gender issues and was bullied by fellow soldiers.
The case is due to last for several more days.