Gates took the stand for the first time on Monday afternoon.
Gates says that when millions of dollars came in from Manafort's Ukrainian consulting work, Manafort would decide whether to classify it as income or a loan. Gates pleaded guilty to financial fraud and to lying to investigators as he negotiated a plea agreement, something defense lawyers will no doubt seize on to try to undercut his credibility.
Experts have billed Gates as the star witness in the tax evasion and bank fraud trial that Special Counsel Robert S. Mueller III is prosecuting against Manafort who is facing 18 counts of tax evasion.
The defense in the case is likely to subject Gates to an intensive cross-examination after arguing during opening statements that he embezzled millions of dollars from Manafort and then turned against him under pressure from Mueller. The usually bearded Gates appeared in court clean-shaven on Monday.
HuffPost Illustration/Getty Images Rick Gates, the star witness in the case against Trump campaign manager Paul Manafort.
Buell also said it's very hard to find a strategy for defending against fraud charges in cases with an extensive paper trail.More news: Luka Modric wants showdown talks over Inter Milan move
"At Mr. Manafort's request. we did not disclose the foreign bank accounts".
Gates also testified he and Manafort knew it was a crime because they had been notified by Manafort's accountants in emails.
Paul Manafort's longtime deputy has been called to the witness stand to testify against the former Trump campaign chairman.
In a court filing on Monday, prosecutors said they may call Federal Bureau of Investigation forensic accountants Morgan Magionos and Renee Michael to read from Manafort's emails.
Paul Manafort's ongoing trial in Virginia, on charges that include bank and tax fraud, may be a sideshow to Special Counsel Robert Mueller's larger Russian Federation investigation, but it produced a pretty compelling moment of courtroom drama on Monday.
On Monday, Ms LaPorta was asked by prosecutors if she had been aware of a $10m loan from Russian oligarch Oleg Deripaska that the district attorney said was "supposedly made in 2006". During that process, Gates admitted to two felony charges, but his testimony would be the first time he details those crimes face-to-face with Manafort, his former boss and mentor.
Earlier Monday, Ellis threatened to kick reporters out of the courtroom if they continue being "disruptive". Mueller is also investigating possible coordination between Trump campaign members and Russian officials in the election campaign, but the charges against Manafort do not address that.