Rick Gates, a longtime business associate of U.S. President Donald Trump's former campaign chairman Paul Manafort, on Monday testified that he helped Manafort file false tax returns and hide his foreign bank accounts.
One part of Gates' testimony led to some laughter in the courtroom.
Some observers who watched Gates' testimony on Monday said they thought he was credible.
Gates, who first met Manafort working for him as an intern fresh out of college, has been described by witnesses as Manafort's right-hand man in his multimillion-dollar political consulting business.
He testified that Mr Manafort had directed him to lower taxable income by reporting overseas income as loans.
On the witness stand Monday, Gates spoke about how he broke the law with Manafort, including by providing false and doctored documents to banks in an effort to inflate Manafort's income to qualify him for loans.
Testifying under immunity, she was the first witness to admit she knew accounting manoeuvrers Mr Manafort and Mr Gates requested of her were wrong and could be crimes.
Manafort has a second trial scheduled for September involving allegations that he acted as an unregistered foreign agent for Ukrainian interests and made false statements to the United States government.
Mr Manafort has pleaded not guilty to 18 counts of bank and tax fraud and failing to disclose foreign bank accounts.
In questioning Ms Laporta on Monday, a prosecutor asked the accountant about a $10 million loan purportedly received by Mr Manafort from Russian businessman Oleg Deripaska in 2006.
Prosecutors have sought to undercut this argument by repeatedly asking witnesses who dealt with Manafort and Gates about the dynamics of their relationship, trying to underscore that Manafort was the supervisor.
He is awaiting sentencing and his ability to secure leniency from the government depends on him being cooperative and forthcoming with the jury. President Trump has previously spoken of the Mueller investigation, referring to it as a "witch-hunt", and reiterating that Manafort only worked for his campaign for a few months. And Trump has shown interest in the proceedings, tweeting support for Manafort.
That's but a drop in the ocean of the roughly $30 million prosecutors are claiming Manafort hid from the IRS.
"If you cause a disruption, I will have you excluded!"
"If at the time you learned Mr. Gates was embezzling millions of dollars from Mr. Manafort, would you have picked up the phone to Mr. Manafort?" He also described in details how he falsified loan applications and other documents to help Manafort obtain more in bank loans.
Four Ukrainian oligarchs funneled money to Manafort's accounts from their own shell companies in Cyprus, Gates testified.
Though the names of those companies appeared on wire transfers and at times on his bookkeeper's ledger, both Manafort's accountants and his bookkeeper say they never knew that the companies - and corresponding offshore bank accounts - were controlled by Manafort.
Manafort's defense hinges on convincing a jury that it was Gates, not Manafort, who committed all of these crimes, and that Manafort is a victim of Gates.
Downing also accused Gates of embezzling "millions", a higher amount than Gates later admitted to in his testimony. Kerik, on the other hand, isn't putting any weight on Gates' words because of his motivation for testifying.