American media are reporting that investigators are unable to prove that WikiLeaks and its colourful figurehead Julian Assange obtained classified US files from jailed soldier Bradley Manning, allegedly the source of most of WikiLeaks' significant material. If true, this is likely to present serious obstacles to US-based criminal proceedings against Assange – though not against Manning.

NBC news, citing unnamed investigating officials, says that US authorities have been unable to find conclusive proof that Wikileaks' vast stashes of secret material – the Baghdad attack-copter videos, Afghanistan and Iraq "war logs" and now the endless mountains of US diplomatic cables being drip-fed by the site – were passed to it by Private Bradley Manning, now being held in a US Marine Corps brig (jail) in Virginia.

Manning has been charged with an array of offences by military prosecutors, including the transfer of classified information onto a personal computer and the adding of unauthorised software to a classified computer system. He is also charged, according to military spokesmen, with "communicating, transmitting and delivering national defense information to an unauthorized source"; "disclosing classified information concerning the national defense with reason to believe that the information could cause injury to the United States"; and "exceeding authorized computer access to obtain classified information".

It has been widely reported that Manning's arrest in Iraq, where he was employed as a junior intelligence specialist at Contingency Operating Base Hammer, resulted from the military authorities being alerted to his activities by a former hacker named Adrian Lamo with whom he had discussed his alleged activities online. Lamo has subsequently said that Manning specifically mentioned various assemblages of data that he planned to leak, including both the gunship videos and diplomatic cables.

Remarks by US defense secretary Robert Gates have since suggested that Manning could not have passed the files he obtained to a third party via the military networks he had access to in Iraq, and it has previously been reported that investigators believe the rogue soldier actually downloaded the data onto CDs, which he may then have physically passed to a contact while on leave in the US.

If this is the case, and assuming adequate care by the files' recipients to sieve out possible security trickery implanted within the data, it would naturally be very difficult to establish to a high standard of proof what happened to the files after they left Manning's hands. Manning himself remains likely to face a lengthy period in military prison if convicted, but it would be difficult to make charges of espionage stick to Assange or other Wikileaks members – assuming they ever found themselves before a US court.

For now, Assange remains bailed under conditions in the UK, where he faces an extradition request from his former base Sweden. Swedish prosecutors want to speak to him regarding allegations of sexual offences made by two women there. Assange is staying at the Suffolk mansion of his admirer Vaughan Smith, a wealthy former Guards officer and journalist. There has been no request thus far for Assange from the USA.

Meanwhile Private Manning is being held as a maximum-security prisoner in the Marine brig at Quantico, Virginia. He is confined to his cell 23 hours a day under conditions which have been condemned as inhumane by human-rights organisations. The brig's commanding officer recently placed the unfortunate soldier on suicide watch, a move which permitted (indeed, required) his jailers to take away his reading glasses and outer clothing, prevent him exercising in his cell and wake him at frequent intervals when asleep.

NBC reports that the suicide watch has now been lifted at the request of US army lawyers, but Manning's maximum-security military prison regime remains an arduous one. Wikileaks has contributed $15,000 to his legal defence fund.

Assange has reportedly signed book deals based on the WikiLeaks affair worth more than £1m, and WikiLeaks itself appears to be a highly lucrative operation, with "seven-figure" weekly revenues mentioned by its payment processor. ®