The US government is pressing ahead with a full-blown prosecution of Bradley Manning, the soldier who has admitted to being the source of the massive WikiLeaks disclosures, even though he has pleaded guilty to charges that carry a top sentence of 20 years.

Army prosecutors have indicated that they intend to proceed with a full court martial against the 25-year-old intelligence analyst in which he will face some of the most serious charges available in a leak case such as this. They include the charge under the Espionage Act that he "aided the enemy" – in practice al-Qaida – by leaking information that ended up on the internet, an accusation that carries possible life in military custody with no chance of parole.

It will be the sixth time the Espionage Act has been unleashed against the source of an official leak of classified information under the Obama administration - more than the total number of times it has been deployed under all previous presidents since it was enacted in 1917.

The soldier has already pleaded guilty to 10 of the 22 charges he is facing, leaving him liable to up to 20 years in military prison followed by a dishonourable discharge. In an exceptionally rare move for a defendant in a serious criminal trial, Manning gave his confession to the court in Fort Meade, Maryland, on Thursday in what is known as a "naked plea" – that is, it was proffered voluntarily and not as part of any plea bargain with the prosecution.

Manning's supporters are now protesting that the soldier has done enough, and that a decision on the part of the prosecution to continue to a full trial would be a blatantly political act. Jeff Patterson, of the Bradley Manning support network, said that "from day one the prosecution had the option to prosecute Bradley easily for the charge's he's admitted to now. If they push on with the Espionage Act it's because they want to send a political message that what Bradley did will not be tolerated."

The team of three military prosecutors presenting the government's case, led by Major Ashden Fein, have thrown the book at Manning. This week they revealed that they intended to call no fewer than 141 witnesses for a possible 12-week trial – a display of prosecutorial muscle that has astonished experts in military law. Eugene Fidell, who teaches military justice at Yale law school, said: "I find it shocking that any trial counsel would think that a judge would permit 141 witnesses. This is not an anti-trust case, there are not that many moving parts in this case."

Among the 141 witnesses, the government intends to call four people who would testify anonymously. They include "John Doe", presumed to be a US Navy Seal who was part of the team that raided the house in Abbottabad, Pakistan, and killed Osama bin Laden.

"Doe" would be called by the prosecution, Fein argued in court this week, to show that Bin Laden personally asked his assistants to access the WikiLeaks disclosures online and present him with their findings. "Doe" is alleged to have grabbed three digital discs in the Abbottabad house on which was stored four-files' worth of WikiLeaks material originating from Manning.

In court on Friday, there was heated legal argument over access to "Doe". According to a court report from Kevin Gosztola of Firedoglake, Manning's lead lawyer, David Coombs, requested permission to interview "Doe" confidentially under pre-trial discovery.

He argued that access was essential for defence to prepare a proper cross-examination strategy over the most serious single charge that the soldier faces. But the prosecution objected, saying that to grant such access could reveal the identity of the unnamed "operator" involved in the killing of the al-Qaida leader.

The invocation of the "enemy" in the Manning trial has potentially huge ramifications for press freedom in the US. In addition to charge 1 that invokes the Espionage Act, specification 1 of charge 2 on Manning's charge sheet, to which he has pleaded not guilty, accuses him of "wrongfully and wantonly [causing] to be published on the internet intelligence belonging to the US government, having knowledge that intelligence published on the internet is accessible to the enemy".

The charge in theory casts a prosecutorial net around any leak of official classified information that ends up on the internet, implying that as it could be accessed by al-Qaida it is therefore aiding the terrorist network. The point was made explicit in the court at Fort Meade when one of the prosecution lawyers was asked whether the same charge could have been brought had Manning leaked to the New York Times instead of WikiLeaks.

"Yes," the prosecutor replied.

The point was not purely hypothetical. It was revealed in Manning's statement, read out to court on Thursday, that he only turned to WikiLeaks after he tried and failed to interest the New York Times and the Washington Post in the classified Iraq and Afghanistan war logs that he had downloaded onto a camera memory stick and brought form Iraq to his aunt's house in Maryland.