WASHINGTON — The Justice Department continued to investigate WikiLeaks last year even after the secret indictment of its founder, Julian Assange, seeking to question at least two of the antisecrecy organization’s volunteers about their activities, according to interviews and a letter obtained by The New York Times.
One day after prosecutors charged Mr. Assange with a single count of conspiracy to unlawfully hack into a computer, the Justice Department asked Daniel Domscheit-Berg, a former WikiLeaks activist, if it could question him about the possibility that he violated American laws prohibiting “the receipt and dissemination of secret information.” The language, in a letter to him in his native German, suggested that prosecutors had not, at least at that point, abandoned the possibility of charges based on WikiLeaks’ publication of United States government secrets.
Prosecutors last summer also sought out David M. House, a former researcher at the Massachusetts Institute of Technology who worked as a volunteer for WikiLeaks from 2009 to 2013.
Mr. House spoke for about 90 minutes to prosecutors and also testified at length to the grand jury, according to a person who has spoken with prosecutors and agreed to an interview on the condition of anonymity. They pressed him for information about debates inside WikiLeaks over whether to redact from government documents posted online the names of vulnerable people, such as foreign citizens who worked confidentially with American military officers or diplomats, to protect them from harm.
The communications with Mr. Berg and Mr. House show that even after Mr. Assange was indicted on accusations of computer hacking, the United States government was eager to build a case against a WikiLeaks associate for disseminating state secrets — a charge that spoke directly to the group’s main enterprise, but would also thrust the Justice Department into a thorny fight over First Amendment rights and galvanize supporters of WikiLeaks and of the free press.
They also show that prosecutors were focused mainly on work done by WikiLeaks in 2010, when Mr. Assange received classified and secret information from Chelsea Manning, a former Army intelligence analyst, about the wars in Iraq and Afghanistan and American diplomacy overseas.
Mr. Assange worked with reporters at publications including The New York Times, The Guardian and the German magazine Der Spiegel to publish that information. Eric H. Holder Jr., then the attorney general, announced a criminal investigation of WikiLeaks.
Justice Department officials under the Obama administration ultimately decided they could not prosecute Mr. Assange for sharing information because it risked setting a precedent that could erode press freedoms for news organizations that also publish classified information.
But prosecutors in Northern Virginia continued to explore ways to crack down on WikiLeaks.
The letter to Mr. Berg, dated March 7, 2018 — one day after Mr. Assange was secretly indicted — was sent by Tracy Doherty-McCormick, a cybercrime and national security specialist who worked on the Assange case while she was a federal prosecutor in Virginia under the Obama administration. She was also the acting United States attorney for the Eastern District of Virginia when Mr. Assange was indicted.
Ms. Doherty-McCormick wrote that the interview would be voluntary, and it was unclear whether Mr. Berg ultimately spoke with prosecutors. The German publication Die Zeit first reported the case against Mr. Berg.
A Justice Department spokesman declined to say whether the government had dropped its case against Mr. Berg or whether there were any sealed charges against him or any other WikiLeaks associates.
In his interviews with prosecutors and the grand jury, Mr. House denied any role in the leak of the documents from Ms. Manning to WikiLeaks, the person said. Mr. House’s interview with prosecutors and grand jury testimony were first reported by The Daily Beast.
He was asked about online chats among WikiLeaks workers that investigators had obtained and was questioned about discussions inside the group about when to redact names from documents posted on the internet.
The question of redactions became a point of contention in 2010, after human rights groups criticized WikiLeaks for exposing the names of Afghan citizens who had assisted the United States and might be subject to retaliation. The group subsequently stripped names from many documents but remained inconsistent in its practices.
It is unclear whether investigators were considering whether endangering people named in the government documents by posting them online might violate a criminal statute.
Mr. Assange was ultimately accused of unsuccessfully helping Ms. Manning try to log onto a classified military network by breaking a passcode and using another person’s identity. He was charged with a single computer hacking offense.
The indictment against Mr. Assange did not include any charge related to the receipt or publication of secret information, but he was accused of hacking into a government computer system “in furtherance of a criminal act” that violated laws against obtaining material to harm the United States or to aid a foreign power.
Nor did the indictment mention the 2016 election or Mr. Assange’s decision to post to WikiLeaks troves of Democratic emails stolen by Russian government hackers.
The special counsel, Robert S. Mueller III, secured an indictment against 12 Russian military officers in the thefts, describing them as part of the Kremlin’s campaign to undermine the American electoral process and help Mr. Trump win the election. The Russians used online personas including Guccifer 2.0 to work with people and organizations in a position to spread the information, including WikiLeaks, according to the indictment.
WikiLeaks’ publication of the stolen Democratic emails may have been omitted from Mr. Assange’s indictment in part because mention of the election could cast the Justice Department’s charges against Mr. Assange in a more political light, legal experts said, and harm the administration’s chances of extraditing him from Britain to stand trial in the United States.