The charges largely predate the five months Manafort spent on Trump's campaign.
Downing questioned why they jury should trust that Gates is telling the truth after all the lies he's told and the crimes he's committed.
Gates knew the underbelly of the entire operation.
Gate's testimony was part of the prosecution's effort to prove that Manafort was responsible for financial maneuverings that he and other witnesses have testified include filing false tax returns, defrauding banks in borrowing against real estate, and failing to report foreign bank accounts.
Gates struggled to answer Downing's questions about which of his transactions were legitimate and which were not, prompting Downing to complain that Gates "seemed to have flawless recollection" when being questioned by Greg Andres, a lawyer for the prosecution.
Mr Gates told jurors that he had been "tasked" by his boss "to determine how we could lower the taxes". He told jurors Manafort classified the money that way to decrease his taxable income.
"Did you submit personal expenses to the inaugural committee?"
Rick Gates, the government's star witness, recounted how he and Manafort used more than a dozen offshore shell companies and bank accounts in Cyprus to funnel the money, all while concealing the accounts and the income from the IRS.
As Gates struggled to answer questions about wire transfers he authorized, Downing pointed out Gates' memory was much clearer when a prosecutor was the one doing the questioning. The defence moved on. After Manafort resigned as the campaign's chairman in August 2016, Gates stayed on and eventually worked on Mr. Trump's inauguration.
Downing also mentioned allegations of insider trading, and discussed Gates' relationship with film producer Steven Brown, who is accused of engaging in a scheme to defraud investors in D-list films. Looking at a ledger listing almost $3 million in transactions, he was unable to say which ones were legitimate and which ones he initiated with false expense reports. He also said he committed credit card and mortgage fraud, falsified a letter for a colleague involved in an investment deal and made false statements in a deposition at Manafort's direction.More news: This researcher wasn’t safe from great white shark
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Gates described in detail his crimes against his employer and even an extramarital affair he'd had, while turning the knife on his longtime boss by outlining the crimes he claims Manafort directed him to commit.
"In Cyprus, they were documented as loans".
Gates was then heard saying Manafort had been on the same path, according to multiple media reports.
Gates' earlier testimony on Tuesday, meanwhile, centered on how Ukrainian businessmen paid Manafort for his consultancy work.
Manafort, the high-powered political consultant, is facing 18 counts and a maximum 305-year prison sentence if the Eastern Virginia jury finds him guilty. But Trump has shown interest in the proceedings, tweeting support for Manafort and suggesting he has been treated worse than gangster Al Capone.
Downing, a former tax prosecutor, also cited a false statement Gates made to the special counsel's office earlier this year before pleading guilty to one count of conspiracy against the USA and one count of making a false statement to the government. Gates testified that Manafort asked him to float Calk, who was on Trump's economic advisory council, for Secretary of the Army.
The case against Manafort has little to do with either man's work for the Trump campaign and there's been no discussion during the trial about whether the Trump campaign coordinated with Russian Federation - the central question Mueller's team has tried to answer.
Gates said he falsely labeled hundreds of thousands of dollars in income as loans to reduce Manafort's tax liability. Gates said he was responsible for collecting all relevant documents for the loan applications.
Downing also asked Gates if he talked to the special counsel's office about his time at the Trump campaign.
"Why is that?" prosecutor Greg Andres asked.