WASHINGTON — A professor with close ties to the Russian government told an adviser to Donald J. Trump’s presidential campaign in April 2016 that Moscow had “dirt” on Hillary Clinton in the form of “thousands of emails,” according to court documents unsealed Monday.
The adviser, George Papadopoulos, has pleaded guilty to lying to the F.B.I. about that conversation. The plea represents the most explicit evidence that the Trump campaign was aware that the Russian government was trying to help Mr. Trump and that the campaign was eager to accept that help.
As part of that effort, the Russian government hacked Democratic accounts and released a trove of embarrassing emails related to Mrs. Clinton’s campaign. The Trump campaign has repeatedly denied any inside knowledge about that.
“They have dirt on her,” the professor told Mr. Papadopoulos, according to the documents. “They have thousands of emails.”
Mr. Papadopoulos was quietly arrested at Washington Dulles Airport on July 27 and has since been cooperating with the special counsel, Robert S. Mueller III, records show. Mr. Papadopoulos’s conversation in April raises more questions about a subsequent meeting in June at Trump Tower, where Mr. Trump’s eldest son and senior advisers met with Russians who were similarly promising damaging information on Mrs. Clinton.
The documents released on Monday said that several senior campaign officials knew about some of Mr. Papadopoulos’s interactions with the Russians. The documents do not say whether he mentioned the Clinton emails to anyone.
The professor, who was not identified in court documents, introduced Mr. Papadopoulos to others, including someone connected to the Russian Ministry of Foreign Affairs and a woman who he believed was a relative of the Russian president, Vladimir V. Putin. Mr. Papadopoulos repeatedly tried to arrange a meeting between the Trump campaign and Russian government officials, court records show.
“We are all very excited by the possibility of a good relationship with Mr. Trump,” the woman, who was not identified, told Mr. Papadopoulos in an email. She was not actually a relative of Mr. Putin, according to court documents.
Mr. Papadopoulos told the F.B.I. in January that the professor was “a nothing.” But Mr. Papadopoulos now acknowledges that he knew the professor had “substantial connections to Russian government officials.” Attempts to reach Mr. Papadopoulos on Monday were not successful.
Mr. Papadopoulos was one of a small group of foreign policy advisers that Mr. Trump announced in March 2016. Another of the advisers, Carter Page, has met with the F.B.I. about his own meetings with Russians.
The plea was unsealed on the same day that Paul Manafort, the former Trump campaign chairman, and his longtime associate, Rick Gates, were indicted on charges of money laundering and conspiracy.
Mr. Papadopoulos was first interviewed by the F.B.I. in January, as the bureau was investigating connections between the Trump campaign and Russia. In that interview, Mr. Papadopoulos said that he began communicating with the professor and the Russian woman before he became a foreign policy adviser to the campaign. He has since acknowledged that is untrue.
“The professor only took interest in defendant Papadopoulos because of his status with the campaign; and the professor told defendant Papadopoulos about the ‘thousands of emails’ on or about April 26, 2016, when defendant Papadopoulos had been a foreign policy adviser to the campaign for over a month,” according to the documents.
In February, Mr. Papadopoulos deleted his Facebook account, which included his communications with the Russians. Later that month, he began using a new cellphone number.
The documents say that Mr. Papadopoulos knew that the professor had met with senior officials in Moscow to discuss Mrs. Clinton’s email.
Mr. Papadopoulos alerted his supervisor and several members of the foreign policy team about his contacts, referring to his “good friend” the professor and a woman he called Mr. Putin’s niece. The campaign supervisor — who was not identified in the documents — said in response that he would “work it through the campaign” and added “Great work.”
The Justice Department said that Mr. Papadopoulos had hurt their investigation.
“Through his false statements and omissions, defendant Papadopoulos impeded the F.B.I.’s ongoing investigation into the existence of any links or coordination between individuals associated with the Campaign and the Russian government’s efforts to interfere with the 2016 presidential election,” the documents said.