George Papadopoulos, a foreign policy adviser to Donald Trump's presidential campaign, pleaded guilty this month to making false statements to FBI agents about his correspondence with Russian nationals and attempts to arrange a meeting between the campaign and Russian officials.

News of the plea came Monday morning, shortly after Trump's former campaign manager, Paul Manafort, and Manafort's longtime business associate Rick Gates were indicted on charges including conspiracy against the United States, money laundering and working as unregistered foreign agents.

More details emerge

Papadopoulos admitted to making false statements and material omissions in January to investigators probing interference in the 2016 presidential election, in relation to his contacts with a London-based professor with ties to the Russian government.

As outlined in the the statement of the offense filing, Papadopoulos met with the professor, who put him in contact with a woman who he believed was a relative of Russian President Vladimir Putin's. Papadopoulos later told Trump that he might be able to arrange for him to meet with Putin. One of Papadopoulos' contacts told him in April 2016 that the Russians "have dirt on" Hillary Clinton, after which he told campaign associates he had "interesting messages coming in from Moscow."

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In an FBI affidavit dated in July — when Papadopoulos was arrested — an agent noted that one of Papadopoulos' contacts sent him an email saying he "just talked to my colleagues from the MFA [Russian Ministry of Foreign Affairs]. [They are] open for cooperating." Papadopoulos responded and said he was "glad the MFA is interested" and forwarded the email to three senior Trump campaign officials.

PHOTO: Special Counsel Robert Mueller departs Capitol Hill following a closed door meeting in Washington, June 21, 2017. (Andrew Harnik/AP) More

After he was interviewed, Papadopoulos deactivated a Facebook account that contained information about his communications with the Russian contacts and stopped using his then-current cellphone number. Since his arrest, he has "met with the government on numerous occasions to provide information and answer questions," according to the plea documentation.

In a statement Monday, attorneys for Papadopoulos declined to comment on the matter, but said they "look forward to telling all of the details of George's story" when called upon by the court.

Manafort and Gates indicted, plead not guilty

Manafort and Gates pleaded not guilty on all charges stemming from special counsel Robert Mueller's five-month-old investigation into Russian meddling in the 2016 election and possible collusion between Trump campaign associates and Russia.

The two surrendered to federal authorities in Washington, D.C., Monday morning after a grand jury approved charges brought by Mueller on Friday. The indictment, which names both men as defendants, contains 12 counts: conspiracy against the U.S., conspiracy to launder money, serving as an unregistered agent of a foreign principal, false and misleading Foreign Agents Registration Act statements, false statements and seven counts of failure to file reports of foreign bank and financial accounts.

PHOTO: Former Trump campaign chairman Paul Manafort leaves federal court, Oct. 30, 2017 in Washington, D.C. (Keith Lane/Getty Images) More

Manafort emerged as a key figure in Mueller's inquiry because of consulting work he did in 2014 on behalf of the Ukrainian government.

In July — the same month he retroactively registered as a foreign agent because of his lobbying work — the FBI executed a search warrant at Manafort's Virginia home, in connection with the Russia investigation. A source familiar with the matter described armed FBI agents' waking Manafort early in the morning as they knocked on his bedroom door.

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