WASHINGTON — The indictment of President Trump’s former campaign chairman captured the top headlines, but a second action by special counsel Robert Mueller may have revealed more about the direction of his secretive investigation.

Mueller signaled Monday that he is aggressively pursuing leads that Trump or those around him may have colluded in Russia’s meddling in last year’s presidential campaign by disclosing a plea agreement with George Papadopoulos, who served as a foreign policy adviser during Trump’s campaign.

Papadopoulos pleaded guilty on Oct. 5 to lying to FBI investigators about his contacts with Russian operatives and is now cooperating with prosecutors.

That may ultimately prove as worrisome for Trump and his lawyers as the action against former campaign chief Paul Manafort and his longtime deputy Rick Gates, who were charged with crimes including money laundering and illegal foreign lobbying.

In combination, the court filings announced by Mueller on Manafort, Gates, and Papadopoulos show that federal investigators have access to years of tax records and international financial information, as well as e-mails and other communications, for officials who served on Trump’s campaign.

The documents also reveal that interactions between the campaign and Russia occurred earlier, and were deeper, than previously documented.

Papadopoulos told investigators that before joining Trump’s campaign he spoke to “an overseas professor’’ who “told him about the Russians possessing ‘dirt’ on then-candidate Hillary Clinton in the form of ‘thousands of e-mails,’’’ according to court documents.

In truth, the court filing said, the conversation occurred after Papadopoulos became a Trump campaign adviser in March 2016, and the “professor only took interest’’ in him “because of his status in the campaign.’’

It said the professor also introduced Papadopoulos to a “female Russian national’’ who was introduced as “a relative of Russian President Vladimir Putin with connections to senior Russian government officials.’’

Papadopoulos told the FBI in January that the professor, who has not been identified, was “a nothing.’’ But Papadopoulos now acknowledges that he knew the professor had “substantial connections to Russian government officials.’’

Papadopoulos alerted his supervisor and several members of the foreign policy team about his contacts, referring to his “good friend’’ the professor.

Trump had named Papadopoulos as one of his foreign policy advisers and called him an “excellent guy’’ in a Washington Post interview in March 2016.

The documents don’t name the campaign officials Papadopoulos communicated with, instead referring to them at various points as a “senior policy adviser,’’ a “high-ranking campaign official,’’ and a “campaign supervisor.’’

In one such example, the court filing said that in April 2016, Papadopoulos e-mailed a high-ranking official of the Trump campaign “to discuss Russia’s interest in hosting Mr. Trump.’’

“The campaign supervisor responded that he would ‘work it through the campaign,’ but that no commitments should be made at that point,’’ according to the document. “The campaign supervisor added: ‘Great work.’ ’’

Similarly, the “statement of the offense,’’ a court filing summarizing the case against Papadopoulos, doesn’t specify whether he ever told anyone on the Trump campaign that Russia had “dirt’’ on Clinton and thousands of e-mails.

Papadopoulos was among those attending a meeting on national security with Trump and other campaign advisers on March 31, 2016, where he said he could help arrange a meeting between the Republican candidate and Putin, the court filing said. No such meeting occurred in the campaign.

In June 2016, Donald Trump Jr., Trump’s elder son, attended a Trump Tower meeting with Russians who had promised dirt on Clinton. Manafort and Trump’s son-in-law Jared Kushner also attended the June meeting. Donald Trump Jr. has said no information of value was provided.

Papadopoulos, 30, faces up to five years in prison and $250,000 in fines. His lawyers, Thomas Breen and Robert Stanley, said in a statement that it was in their client’s best interest that they “refrain from commenting on George’s case.’’

Under the plea agreement with prosecutors, he is likely to serve no more than six months and may avoid prison entirely.

White House press secretary Sarah Sanders dismissed Papadopoulos’s role in Trump’s campaign, telling reporters Monday that “it was extremely limited. It was a voluntary position.’’ She said “no activity ever was done in an official capacity on behalf of the campaign.’’

Democrats quickly seized on the new revelations.

“We now know that the Trump team was approached multiple times with information about the Russian campaign to damage Hillary Clinton, and in each case, they appear to have welcomed the help,’’ Adrienne Watson, a spokeswoman for the Democratic National Committee, said in a statement.

“Trump can no longer claim there is no evidence of collusion between his campaign and Russia,’’ Watson said.

US intelligence agencies have found that Russia interfered in last year’s campaign with the goal of hurting Democrat candidate Clinton.

The president has at times questioned that conclusion and has called the investigations into possible collusion with Russia a “witch hunt.’’