Retired Lt. Gen. Michael Flynn told investigators that "senior campaign officials" discussed reaching out to WikiLeaks, according to a newly unsealed document from special counsel Robert Mueller.

Flynn, who served on President Trump's campaign and briefly served as national security adviser, sat for 19 interviews with Mueller's team before and after he pleaded guilty to lying to the FBI about his contacts with a Russian envoy.

The document, unsealed on Thursday, is an addendum to the government's memo in aid of sentencing Flynn, said he "provided useful information concerning discussions within the campaign about WikiLeaks’ release of emails."

During the 2016 election, WikiLeaks released emails stolen from the Democratic National Committee and John Podesta, the chairman of Hillary Clinton’s 2016 presidential campaign. Mueller's 448-page report, released last month with redactions, cites substantial evidence showing Russian actors hacked Democratic email accounts and gave the thousands to WikiLeaks to disseminate.

The document unsealed on Thursday goes on to describe in sparse detail how Flynn helped on this topic.

“The defendant relayed to the government statements made in 2016 by senior campaign officials about WikiLeaks to which only a select few people were primary," Mueller wrote. "For example, the defendant recalled conversations with senior campaign officials after the release of the Podesta emails, during which the prospect of reaching out to WikiLeaks was discussed.”

It is unclear who these "senior campaign officials" might be. A February court filing from prosecutors in February said Mueller has communications between longtime Trump associate Roger Stone and WikiLeaks. Stone briefly served as an adviser to the campaign but was not seen as a top official.

Stone was charged in January with lying to Congress, witness tampering, and obstructing the special counsel’s investigation into Russian interference in the 2016 election. The 66-year-old pleaded not guilty to all charges. Prosecutors said at the time that Stone lied about his communications with WikiLeaks and senior Trump campaign officials and that their evidence of wrongdoing was “both voluminous and complex.”

Mueller's unsealed document also describes for Flynn provided "firsthand information about the content and context of interactions between the transition team and Russian government officials" and "assisted" the investigation into potential obstruction of justice by Trump.

Last month, WikiLeaks founder Julian Assange, 47, was arrested at the Ecuadorian Embassy in London in connection to a charge in the U.S. of conspiring to hack into a Pentagon computer network in 2010.

An unsealed indictment revealed Assange had not been charged in connection with Russian interference in the election nor had he been charged for publishing government secrets contained in the documents leaked by former Army intelligence analyst Chelsea Manning almost a decade ago. Instead, prosecutors charged him with conspiracy to commit computer intrusion by agreeing to help Manning crack a password that would have given her access to a classified military network.

The single-count conspiracy indictment against Assange carries a maximum penalty of five years in prison, but national security experts speculate that there could be a slew of additional charges — including espionage — leveled at Assange if and when he is extradited to the United States. Assange must face extradition proceedings in the United Kingdom before he is potentially brought to the U.S.

Flynn has yet to be sentenced and is still working with Justice Department prosecutors in criminal case against Bijan Kian, his former lobbying partner who worked for the Turkish government. Flynn faces up to five years in prison.