Washington (CNN) Former Donald Trump campaign official Rick Gates pleaded guilty Friday to two criminal charges in special counsel Robert Mueller's wide-ranging investigation of Russian meddling in the 2016 presidential campaign and related activities.

Gates is now the third Trump associate known to be working with Mueller's investigation, and his plea deal will put the spotlight on former Trump campaign chairman Paul Manafort.

Prosecutors may try to pressure Manafort to speak with them about what he knows, particularly about the campaign.

As part of Gates' agreement, which dismisses a handful of money laundering and other criminal charges, Gates will have to cooperate with the special counsel by turning over all documents relevant to the investigation, speak with investigators as they wish and possibly testify in other court cases, including Manafort's. Gates may also even be asked to go undercover.

Gates, 45, was Manafort's right-hand man for a decade, was privy to most, if not all, of Manafort's activities during the campaign and stayed in the Trump orbit after Manafort's exit.

Manafort has vowed to fight his charges and could be central to Mueller's investigation of the Trump campaign's ties to Russia, given his connection to both Trump and rich and powerful Russia-sympathetic Ukrainians. He has pleaded not guilty.

"I continue to maintain my innocence," Manafort said in a statement Friday after Gates' plea deal. "I had hoped and expected my business colleague would have had the strength to continue the battle to prove our innocence. For reasons yet to surface he chose to do otherwise. This does not alter my commitment to defend myself against the untrue piled up charges contained in the indictments against me."

Last Friday, the special counsel produced grand jury indictments for 13 Russian nationals, accusing them of operating a misinformation campaign to hurt Hillary Clinton's presidential effort. Former national security adviser Michael Flynn and Trump campaign adviser George Papadopoulos have already pleaded guilty to lying to investigators about their interactions with Russians and agreed to cooperate.

The 'scheme'

In court and case filings, prosecutors described an 11-year "scheme" in which the two longtime business partners allegedly worked together to launder tens of millions of dollars they made doing foreign lobbying work, avoid paying taxes and buoy income with fraudulently obtained loans.

Gates said he was guilty of helping Manafort use bank accounts in Cyprus and Grenadines to hide millions of dollars they made lobbying for Ukrainian politicians as far back as 2006.

The pair flowed $75 million through offshore accounts, and Manafort laundered $18 million to buy property and luxury goods in the US, prosecutors said. Gates transferred $3 million between accounts, court papers said.

Manafort also used the bank accounts to buy real estate in the US and obtain mortgages, prosecutors charge.

Throughout the 45-minute plea hearing Friday in Washington, prosecutors framed Gates as an assistant in criminal activity, doing Manafort's bidding.

"Acting on the authority of Mr. Manafort, [Gates] routinely dealt with Mr. Manafort's tax accountants" and misled them, prosecutor Greg Andres described to the judge. Manafort also lied on his foreign lobbying registrations "with Gates' assistance," prosecutor Andrew Weissmann said.

Gates, bearded and wearing a blue suit, tie and cuff links, listened as Judge Amy Berman Jackson read the offenses he is agreeing to plead guilty to. He said, "Yes, your honor," repeatedly as she read the court documents.

As he exited the hearing, Gates appeared in a lighter mood. He briefly joked with reporters about whether he may shave his beard, then walked from the courthouse to a waiting SUV through a scrum of cameras and protesters.

Gates has agreed to cooperate with prosecutors, and they may ask the judge to reduce his sentence if they are satisfied. Gates' attorney also told the court he may argue for a reduction of the sentence because of the "disproportionate conduct" between Manafort and Gates.

Gates faces a maximum sentence of 10 years in prison, but it's more likely his sentence will range from almost five to six years, the judge said. His charges together also carry a maximum fine of $500,000, though it's more likely his fine will range from $2,000 to $200,000, according to the judge. A hearing date for Gates' sentencing has not been set.

Earlier Friday, Gates said that despite his "initial desire to vigorously defend myself," he has had a "change of heart" in order to protect his family, according to a letter sent to his family and friends, obtained by CNN from a Gates friend.

"The reality of how long this legal process will likely take, the cost, and the circus-like atmosphere of an anticipated trial are too much," Gates wrote. "I will better serve my family moving forward by exiting this process."

The father of four wrote that it was a "difficult decision" to make, but that ensuring his family's well-being "is first and foremost."

"The consequence is the public humiliation, which at this moment seems like a small price to pay for what our children would have to endure otherwise," he said.

Document says Gates lied this month about Ukraine discussion

One new charge Friday zeroed in on a conversation Gates had with investigators earlier this month about Manafort's Ukrainian lobbying.

Gates lied to investigators earlier this month about a 2013 meeting in Washington attended by Manafort and others. According to the document, Gates lied when he said Ukraine was not discussed at the meeting.

"Gates had participated with Manafort in preparing a report that memorialized for Ukraine leadership the pertinent Ukraine discussions that Manafort represented had taken place at the meeting," the new court filing says.

That meeting, in mid-March 2013, was attended by Manafort, California Rep. Dana Rohrabacher and former Rep. Vin Weber, who is now a lobbyist with Mercury LLC, according to lobbying disclosures filed last year with the Justice Department. Rohrabacher and Weber were not identified in Friday's court filings, though their positions were referenced and the description in the court filing matches the record of the meeting in the lobbying disclosures.

Rohrabacher is one of the most Russia-friendly lawmakers on Capitol Hill. He regularly embraces Kremlin-aligned talking points and has forged friendly relations with WikiLeaks founder Julian Assange. Rohrabacher has given private interviews to the Senate and House Intelligence committees, which are conducting their own investigations into Russian meddling in the 2016 election.

Rohrabacher spokesman Ken Grubbs acknowledged that the congressman attended the meeting with Manafort and Weber.

"The three reminisced and talked mostly about politics," Grubbs said in a statement about the 2013 meeting. "The subject of Ukraine came up in passing. It is no secret that Manafort represented Viktor Yanukovych's interests, but as chairman of the relevant European subcommittee, the congressman has listened to all points of view on Ukraine."

Grubbs also told CNN that Mueller's office has not had any contact with Rohrabacher.

Mercury said it had acted appropriately and was cooperating with Mueller.

"Rick Gates' pleaded guilty to making false statements today. He admitted that he didn't tell the truth to the Government and didn't tell the truth to our lawyers when he spoke to them about this project," Mercury said in a statement. "While he and others involved with this matter may have acted criminally and tried to hide it, we have acted appropriately, following our counsel's advice from the start."

Prosecutors allege that Manafort's lobbying in the US on behalf of Ukraine went even further in 2013. He allegedly orchestrated a group of former European politicians, called the "Hapsburg group," to act as independent voices, then paid them to push positions favorable to Ukraine.

Manafort used offshore accounts to pay the former politicians 2 million euros, a new indictment against Manafort said Friday. They lobbied members of Congress and members of the executive branch in the US around 2013.

Manafort also allegedly used $4 million from an offshore account to fund a report on the trial of a political opponent jailed by his clients. A lawyer involved in the report pleaded guilty to lying to investigators earlier this week.