The defence has rested its case in the trial of the WikiLeaks source Bradley Manning, rounding off its portrayal of the US soldier as a young man who accepted that he was wrong to have leaked a vast trove of state secrets but who had no "general evil intent" to "aid the enemy".

Having called just 10 witnesses over the space of three days, the defence phase of the trial was brought to a close far quicker than expected. The defence had indicated in earlier hearings that it intended to call more than 40 witnesses, although many may yet still be presented in court during the post-verdict sentencing stage of the court martial.

By contrast, the prosecution took 14 days to make its case, drawing on 80 witnesses.

On Wednesday, the defence team lead by the civilian lawyer David Coombs, focused its attentions on the most serious charge facing the Army private – that he "aided the enemy" by transmitting information to WikiLeaks knowing that it would be accessible to enemy groups notably al-Qaida. Manning faces a possible sentence of life in military custody with no chance of parole under this single charge.

The final defence witness called, the Harvard law professor Yochai Benkler, delivered blistering testimony in which he portrayed WikiLeaks as a legitimate web-based journalistic organisation. He also warned the judge presiding in the case, Colonel Denise Lind, that if the "aiding the enemy" charge was interpreted broadly to suggest that handing information to a website that could be read by anyone with access to the internet was the equivalent of handing to the enemy, then that serious criminal accusation could be levelled against all media outlets that published on the web.

Benkler, who is co-director of the Berkman Center for Internet & Society at Harvard, was accepted by the court as an expert on the future of journalism in the digital age, despite prosecution attempts to have him disqualified. Under defence questioning, according to a transcript of the court proceedings provided by the Freedom of the Press Foundation, Benkler roundly dismissed any connection between WikiLeaks and terrorist organisations and damned as "a relatively mediocre effort" a counter-intelligence report titled "Wikileaks.org – An Online Reference to Foreign Intelligence Services, Insurgents, or Terrorist Groups?".

The US government has leant heavily on that report in making its case against the army private, telling the court that there had been forensic evidence that Manning had accessed the document on several occasions. But Benkler said that the report did the opposite of what the government intended – it showed WikiLeaks in the light of a journalistic organisation: "In many places it describes WikiLeaks staff as writers or editors," he said.

Benkler told the court that in his reading of the Pentagon report, "there is little doubt that [WikiLeaks] is a journalistic, hard-hitting journalistic investigative organisation".

Amid the legal argument over Benkler's expert credentials, one of the great ironies of the Manning trial emerged in court. In seeking to drive home the "aiding the enemy" charge, the government has presented evidence gathered during the 2011 raid in Abbottabad, Pakistan, in which Osama bin Laden was killed, that the al-Qaida leader personally requested Wikileaks material to read.

But Coombs revealed in court that according to stipulated testimony that has not yet been made public, Bin Laden only asked to see the WikiLeaks files after his curiosity was piqued by the US government's own description of WikiLeaks as an organisation helpful to America's enemies. It was the government's own rhetoric, Coombs said, that drew the al-Qaida chief's attention to the website; the defence attorney said this was an important example of how a legitimate journalistic organisation could be turned into a terrorist outfit "upon response of the government".

The "rhetoric is what drives the enemy to actually go look at WikiLeaks, not the actual publication of the information," Coombs said.

With the close of the defence case, the trial now moves rapidly towards its climax. On Monday, legal argument will open over four defence motions to have seven of the 22 counts against Manning dismissed on grounds of lack of evidence or inappropriate use of charges. The prosecution has also asked permission to rebut the defence case that the soldier had no actual knowledge that by leaking to WikiLeaks he was causing damage to the US – a key element in several of the most serious charges including "aiding the enemy" and counts brought under the 1917 Espionage Act.

In his opening statement, Coombs described Manning as a naive but well-intentioned young man who had no desire to harm his country. In the course of legal argument over Benkler's testimony, the defence lawyer added that "the actual release was wrongful, and he's accepted responsibility for that. But it was not wanton."