The highly anticipated criminal trial of two companies owned by former President Donald Trump began Monday in New York State Supreme Court, with much of the attention focused on one of Trump's most loyal deputies, former Trump Organization Chief Financial Officer Allen Weisselberg.

Prosecutors promised Weisselberg, who pleaded guilty to 15 charges of fraud in August, will reveal insider details on the alleged scheme to dodge taxes. The companies' defense attorneys said he acted to benefit himself, not the Trump family businesses, according to media reports from the Manhattan courtroom.

In what is expected to be a six-week-long trial, The Trump Corp. and another family company, Trump Payroll Corp., are answering to charges of criminal tax fraud, as well as falsifying business records and filing false tax returns. Neither Trump nor any of his children have been charged with any crimes.

“This case is about greed and cheating, cheating on taxes,” Susan Hoffinger, the chief of investigations for Manhattan District Attorney Alvin Bragg, told the jury during the first day of the trial on Monday, Politico reported. “The scheme was conducted, directed and authorized at the highest level of the accounting department.”

The companies and Weisselberg were charged last summer, when state prosecutors formally accused the firm of finding illegal ways to avoid state, local and federal taxes in a 15-year scheme. As part of Weisselberg's plea deal, he  agreed to testify at the trial. Weisselberg, the prosecutors said, had benefited from some $1.76M in “indirect employee compensation," which involved money to pay for schools for his grandchildren, as well as luxury cars and apartments.

The Manhattan District Attorney’s Office case is that the Trump companies gained from Weisselberg’s impropriety, as the firm paid taxes on lower salaries. Defense lawyers, however, argued that Weisselberg’s actions were his own, only benefited himself — and there was no wrongdoing at the company.

“What the prosecutors have not made clear to you is that the person at the Trump Corporation who is responsible for instructing that all of this income not be reported is none other than Mr. Weisselberg himself,” defense attorney Susan Necheles said, according to The New York Times.

Weisselberg is yet to be sentenced, and while he did not provide evidence into the investigation of the company, Assistant District Attorney Joshua Steinglass said in August he would recommend a harsher state prison term if Weisselberg doesn’t take the stand and tell the truth. If found guilty, the company would face a maximum $1.62M fine.

The trial begins as New York Attorney General Letitia James pursues a civil fraud lawsuit against the former president, his businesses and his three eldest children. In September, she asked a state court to ban the Trumps from working in New York real estate for five years.