Rick Gates, a former aide to President Trump's campaign and a central figure in special counsel Robert Mueller's investigation, was expected to plead guilty as early as Friday, according to a person familiar with the matter who was not authorized to comment publicly.

Gates and Trump's former campaign chairman Paul Manafort were indicted in October on charges that they secretly worked on behalf of a pro-Russian political faction in Ukraine and laundered $4 million in payments through overseas bank accounts. The political work pre-dated their work on Trump's campaign, but prosecutors charged that they sought to cover up their Ukraine connections while working for Trump.

Prosecutors working for special counsel Robert Mueller launched another barrage against the men on Thursday, revealing a 32-count indictment in Virginia that accused them of defrauding banks to obtain millions of dollars worth of loans, and of laundering more $30 million in income through offshore bank accounts to conceal it from U.S. tax authorities.

Gates was expected to plead guilty to at least some of the charges.

Gates would become the fifth person to plead guilty to a crime in special counsel Robert Mueller's investigation of Russian meddling in the 2016 election.

Prosecutors also have secured guilty pleas from Trump's former national security adviser Mike Flynn and a campaign foreign policy aide, George Papadopoulos, who acknowledged in court documents that he met with a person he thought was tied to the Russian government who was offering "dirt" on Trump's political rival, Hillary Clinton.

A guilty plea by Gates – particularly if it was to be accompanied by a promise to cooperate with investigators – would put an even tighter legal squeeze on Manafort, who played a key role in some of the episodes that have been of particular interest to investigators, including a 2016 meeting between Trump's son Donald Trump, Jr. and a Russian lawyer offering damaging information about Clinton.

Manafort pleaded not guilty to Mueller's first round of charges, which were filed in Washington in October. The new case against Manafort and Gates, filed in Virginia, remained mostly under seal on Friday morning.