"In essence, I was living beyond my means", the married father of four said from the witness stand in Alexandria, Virginia.
"I'm here to tell the truth and take responsibility for my actions", Gates said in response to a question from Downing about his trustworthiness. "You said you had a made mistake", the lawyer said.
Manafort is the first person to be tried on charges brought by special counsel Robert Mueller's investigation into Russian interference in the 2016 US presidential election.
Gates embezzled hundreds of thousands of dollars from Manafort by filing exaggerated - and at times, completely fabricated - expense reports, Downing forced him to admit Tuesday.
Gates appeared shaky at times in answering questions, contrasting sharply with his firm and clear answers to questions by prosecutors. "Did you provide false information or did you have a bad memory?" he asked.
"After all the lies you've told, and the fraud you've committed, you expect the jury will believe you?"
"No, I did not", Gates responded.
For this Manafort was paid US$4million a year, in quarterly payments of US$1million, Gates recalled, though at some point the currency switched from U.S. dollars to Euros.
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On Wednesday, Gates initially testified Manafort told him to be truthful during a 2014 interview with the Federal Bureau of Investigation about offshore shell companies and bank accounts that contained millions of dollars in proceeds from their Ukrainian political work.
The charges largely predate the five months Manafort spent on Trump's campaign.
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. 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.
Gates also admitted, however, that the same tricks he used to help doctor and falsify records for Manafort he also deployed for his own personal gain in order to covertly wire funds out of Manafort's offshore accounts to line his own pockets.
With a nod to linguistic differences for what Americans refer to as an apartment, Downing pressed: "As part of your secret life did you maintain a flat - is that what they call it? - in London?"
Gates said he did not.
Prosecutors hope to wrap up their case this week.
Gates's testimony against Mr Manafort marked a shattering end to a relationship that made the two political consultants millions working for foreign politicians and led them both to prominent positions on the Trump campaign. "Mr Manafort worked with the local political officials and helped implement policy initiatives based on the campaign promises". Gates also said Manafort floated banker Stephen Calk's name for consideration as Secretary of the Army, a post he ultimately did not get.
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Rahn declined to say at the time whether investigators have found her FitBit or if they know its location. Tibbetts hasn't been seen since July 18, when she went for a run in her small hometown of Brooklyn, Iowa.
Employees from Federal Savings Bank are expected to testify later this week.
In October 2016, for instance, Gates sent Manafort DMP's profit and loss statement (P&L) from January 1 through June 30 of that year, emails introduced in court Tuesday show.
But that changed Tuesday during a full day of testimony by Rick Gates, the prosecution's star witness and another former member of the campaign.
"Mr. Manafort requested. that we did not disclose foreign bank accounts", Gates testified. "I'm here", Gates said from the witness chair. Walter Mack, Brown's lawyer, declined comment.
Prosecutors showed contracts laying out that Manafort would be paid $4 million a year in quarterly installments of $1 million, all channeled through Cyprus.
Prosecutors had intentionally left many of these pieces of evidence blank on an itemized list of documents they are presenting in court, signaling they could be the most sensational and attention-grabbing files in the evidence binder.
On Tuesday, Gates did connect one part of the bank fraud charges against Manafort to his role in the Trump campaign.
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Samsung said it also made a decision to hand out dividends of 354 won per shares, with the combined amount of 2.4 trillion won. Samsung Electronics plans to showcase the Galaxy Note 9 smartphone on august 9 and start full-fledged sales later in the month.