Gates, who also served in a senior role in Donald Trump's presidential campaign, is expected to face aggressive cross-examination once prosecutors are finished questioning him.
Gates pleaded guilty to financial fraud and to lying to investigators as he negotiated a plea agreement, something defence lawyers will no doubt seize on to try to undercut his credibility.
He is awaiting sentencing and his ability to secure leniency from the government depends on him being cooperative and forthcoming with the jury.
The criminal case has nothing 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 Russia — the central question Mueller's team has tried to answer.
But Trump has shown interest in the proceedings, tweeting support for Manafort and suggesting that he had been treated worse than gangster Al Capone.
The trial opened last week with a display of Manafort's opulent lifestyle, then progressed into testimony about what prosecutors say were years of financial deception.
In calling Gates, the government will present jurors with the firsthand account of a co-conspirator expected to say Manafort was knee-deep in an alleged scheme to hide millions of dollars from the IRS and defraud several banks.
During the questioning, US District Judge T.S. Ellis will be both referee and wild card. He has played those roles throughout the trial, repeatedly scolding prosecutors to rein in their depictions of Manafort's lavish lifestyle and demanding that they "move it along." It is not a crime, he has said several times, to be rich and to spend ostentatiously.
Nonetheless, jurors were told of more than US$900,000 in expensive suits, a US$15,000 ostrich jacket and lavish properties replete with expensive audio and video systems, a tennis court encircled by hundreds of flowers and, as one witness put it, "one of the bigger ponds in the Hamptons."
One by one, a retired carpenter, a natty clothier and a high-end landscaper detailed how Manafort paid them in international wire transfers from offshore companies.
Prosecutors say Manafort used those companies to stash millions of dollars from his Ukrainian consulting work, proceeds he omitted year-after-year from his income tax returns. Later, they say, when that income dwindled, Manafort launched a different scheme, shoring up his struggling finances by using doctored documents to obtain millions more in bank loans.
All told, prosecutors allege that Manafort failed to report a "significant percentage" of the more than US$60 million they say he received from Ukrainian oligarchs. They sought to show jurors how that money flowed from more than a dozen shell companies used to stash the income in Cyprus.
Though the names of those companies appeared on wire transfers and at times on his book-keeper's ledger, both Manafort's accountants and his book-keeper say they never knew that the companies — and corresponding offshore bank accounts — were controlled by Manafort.
When they appeared, the book-keeper and accountants said, they thought the companies were clients or, in some cases, lenders.
But defence lawyers are trying to convince the jury that Manafort was consumed by his consulting business and left the particulars of his finances to professionals and, in particular, to Gates.
- AP
