Military prosecutors sought to link US Army intelligence analyst Bradley Manning directly to WikiLeaks founder Julian Assange Monday at a hearing to determine whether Manning will be court-martialled in the biggest leak of classified documents in American history.

Computer forensic investigators Mark Johnson and David Shaver told the hearing they had found logs from an online chat between Manning's account and an account which at one point was alleged to be connected to Assange. The logs discussed sending and receiving US government information.

Asked if Manning and Assange seemed to know each other, Johnson said they did. "At some point I believe they talked about: 'Did you receive information?' Where would that come from if they hadn't known each other in the past," Johnson said.

The 24-year-old Manning is suspected of downloading thousands of classified or confidential documents from the military's Secret Internet Protocol Router Network, or SIPRNet. Those files are thought to have later appeared on WikiLeaks.

On Monday, the government completed the fourth day of a hearing to determine whether there is sufficient evidence to court martial Manning on 22 charges, which include aiding the enemy and unlawfully causing intelligence to be published on the Internet. Manning faces life imprisonment if convicted of the most serious charge.

Prosecutors have portrayed Manning as a well-trained soldier adept at computers who violated his duties. Manning's defense lawyers have presented evidence he was emotionally troubled and have questioned why he was not relieved of his intelligence duties sooner.

Witnesses have said Manning sent an email to his sergeant saying confusion over his gender identity was seriously hurting his life, work and ability to think. Manning had created a female alter-ego online, Breanna Manning, according to testimony at the hearing.

Assange does not presently face charges in the United States related to publication by WikiLeaks of hundreds of thousands of pages of US military reports and State Department cables.

But a federal grand jury in Alexandria, Virginia, has been collecting evidence on Assange and his associates for months. A department spokesperson acknowledged on Monday that the Justice Department has an ongoing investigation related to Assange.

Assange is in Britain fighting extradition to Sweden for questioning about accusations of rape and sexual assault made by two female former WikiLeaks volunteers in August 2010. Last week, Britain's Supreme Court agreed to hear an appeal by Assange against the Swedish extradition request.

In testimony at Manning's hearing on Monday, Johnson said he searched the private's personal computer and found portions of a deleted file in an easy-to-transfer format with progress reports indicating data was being sent to the WikiLeaks upload page.

He also found an "upload complete" indicator, signaling a successful transfer, Johnson said.

One of Manning's memory cards shipped from Iraq contained four bundled files in easy-to-transfer format, including one with 91,000 Afghanistan reports and another with 400,000 Iraq reports, they said.

Shaver said a text file named README.txt included in the bundle said: "These are items of historical importance for two wars in Iraq and Afghanistan, significant activity, sigacts between 0000 1 Jan 2004 and 2359 31 Dec 2009."

SIGACTS are militarily significant activity reports that discuss enemy actions, tactics, techniques and procedures.

"These items have already been sanitized from any source identification," the file said. "You might want to sit on this information from 90 to 180 days to decide how to best send and distribute data to a large audience. ... This is possibly one of the most significant documents of our time."

The investigators also said they found an email communication between Manning and a person named Eric Schmiedl in late May 2010, in which Manning says: "I was the source of the 12 Jul 07 video from the Apache weapons team, which killed two journalists and injured two kids."

Investigators have said they found two versions of the Apache helicopter gunsight video on Manning's classified work computer, one of which appeared to be one aired by WikiLeaks and another that may have been the source material.

The video showed an attack that killed several Iraqis, including two Reuters journalists.

The investigators testified that Manning cleaned out his personal Apple MacBook Pro in January. "Everything form early January and prior is gone, permanently erased," Johnson said.