WASHINGTON – Special counsel Robert Mueller unveiled criminal charges Monday against three senior aides to President Trump's 2016 campaign, the first prosecutions to come from an investigation of Russian interference in the presidential election.

In one case, a federal grand jury charged that Trump's former campaign chairman Paul Manafort and his associate Rick Gates worked secretly to influence the U.S. government on behalf of pro-Russian factions in Ukraine, then laundered their profits through a series of overseas businesses and bank accounts.

In another case, former campaign foreign policy adviser George Papadopolous pleaded guilty to charges that he lied to FBI agents investigating Russian election meddling. The former Trump adviser acknowledged in his October 5 guilty plea that he

met with a Russian professor and a woman he described in an email as Russian President Vladimir Putin's niece after joining the campaign.

Mueller's office filed the charges against Papadopolous in July, but the charges had remained under seal until Monday morning. Mueller's office also arrested Papadopolous in July, when he landed in the United States after at trip to Germany, according to court records. Mueller's office asked a judge in Washington to keep the charges secret because his arrest "could alert other subjects to the direction and status of the investigation."

Trump downplayed the charges Monday. "Sorry, but this is years ago, before Paul Manafort was part of the Trump campaign. But why aren't Crooked Hillary & the Dems the focus?????," he wrote on Twitter. "Also, there is NO COLLUSION!"

The charges against Manafort and Gates include 12 counts of conspiracy, money laundering, failing to register as foreign agents and making false statements to investigators. Many of the charges are based on Manafort and Gates' work for the government of Ukraine, which began long before both men joined Trump's presidential campaign.

Manafort and Gates were scheduled to appear in federal court on Monday afternoon.

Mueller had been investigating Manafort, who resigned as Trump’s campaign chairman in August 2016, for his financial ties to a pro-Russia party in Ukraine.

The indictment makes no reference to Manafort's work on Trump's campaign. But it alleges that Manafort's efforts to conceal his work on behalf of Ukraine continued while he was running the campaign. As late as Aug. 19, 2016, three days before Trump fired him, the indictment alleges that Manafort and Gates sent "false talking points" to one of the political consulting firms they had hired to lobby on behalf of pro-Russian factions in Ukraine.

Rather, prosecutors allege that for more than a decade, Manafort and Gates worked secretly to influence the U.S. government on behalf of pro-Russian factions in Ukraine, then laundered their profits through a series of overseas businesses and bank accounts. In all, prosecutors alleged that $75 million passed through offshore bank accounts that the men controlled.

Manafort "used his hidden overseas wealth to enjoy a lavish lifestyle in the United States," prosecutors wrote. Investigators traced wire transfers from bank accounts in Cyprus to that Manafort allegedly used to pay his landscapers and to buy a Mercedes and a Range Rover. Prosecutors also said that he used the accounts to pay more than $1.3 million to clothing stores in New York and Beverly Hills.

A spokesman for Manafort could not be reached to comment Monday morning.

Manafort has long been a central figure in Mueller's investigation. FBI agents raided his apartment over the summer. He has come under scrutiny both for his work in Ukraine and his participation in a meeting in 2016 between Donald Trump, Jr. and a Russian lawyer promising damaging information about Hillary Clinton.

According to the indictment, Manafort and Gates began working on behalf of Ukraine's pro-Russian government in 2006.

When U.S. authorities made inquiries about the payments last year, Manafort and Gates responded "with a series of false and misleading statements."

Gates had worked with Manafort in the private sector and followed him to Trump's campaign in 2016. Gates wound up moving to the Republican National Committee when Manafort was ousted from the campaign, and he helped set up a pro-Trump super PAC after the election.