"One thing I know a lot about is the legal definition of fraud," Justice Arthur Engeron said as he gaveled court into session prior to the start of opening statements.

Engoron opened the proceedings after allowing cameras in to document the scene in the courtroom: Trump, arms folded, flanked by his legal team; Engeron on the bench; and throngs of reporters and spectators in the gallery.

"I've promised to do my best despite my lame attempts at humor," Engeron said in a brief opening statement. "I take my job very seriously."

The trial is expected to last through Dec. 22, Engeron said, and suggested he would attempt to keep a low profile after today.

"For the next three months, I hope the only words I will mutter are 'Sustained,' 'Overruled,' and 'Let's take a 10-minute break,'" he said.

Opening statements are underway in former President Trump's $250 million fraud trial.

Trump is seated between his attorneys Clifford Robert, Alina Habba and Christopher Kise.

Trump and his co-defendants face a bench trial, meaning that the sole arbiter of the case is Judge Arthur Engoron instead of a jury.

Former President Trump has taken a seat in the courtroom for the start of the trial.

"The crime is against me," he told reporters outside the courtroom before he made his way inside.

He denounced the case in now-familiar terms, criticizing state Attorney General Letitia James as she sat inside the courtroom.

Trump also accused Judge Arthur Engoron of failing to account for the full value of his real estate portfolio, asserting his Mar-a-Lago estate is worth "50 to 100 times more" than the judge's decision for partial summary judgment said last week.

"We have other properties, the same thing. So he devalued everything," Trump said. "We have among the greatest properties in the world. and I have to go through this for political reasons."

Engoron decided Trump's statements of financial condition were fraudulent, but Trump said, "We have a clause in the contract that says, essentially, buyer beware."

Former President Trump, speaking to reporters on his arrival at the lower Manhattan courthouse, said the trial is a witch hunt resulting from his standing in the presidential polls.

"This is a continuation of the greatest political witch hunt of all time," he told reporters outside the courtroom.

Trump said he is innocent of the accusations and that his portfolio has a much higher value than what the attorney general alleges.

Patrick Birney had been working for the Trump Organization for more than two years when a magazine article prompted him to change Trump's financial statement, the executive testified.

"There was an article written that stated that Mr. Trump's triplex was actually 10,900 or so square feet," Birney said, referring to a 2017 Forbes magazine article that alleged Trump had been lying about the size of his residence. (Judge Engoron decided in his partial summary judgment last month that the size was misrepresented.)

Birney, who was an assistant VP at the time, testified that Trump Organization executives, including former CFO Allen Weisselberg, "verified" the size and adjusted the next year's statement of financial condition. As a result, the penthouse was valued at $116 million in 2017 -- a steep drop from the 2016 valuation of $327 million.

Birney testified that he looked up comparable properties to come up with the value of the apartment going forward.

"I Google searched recent penthouse sales in Manhattan," Birney said, eventually landing on an web article about a penthouse purchased by billionaire Ken Griffin that set the record for most expensive home ever sold in the United States.

A price-per-square-foot for Trump's penthouse was determined based on that record-breaking sale, Birney said.

When Birney was tasked with finding comparable properties to value Trump's Mar-a-Lago Club, he similarly searched for nearby Palm Beach homes. However, Trump signed a deed in 2002 that limited Mar-a-Lago's purpose to a social club, the New York attorney general alleges, making the price of nearby residences irrelevant.

Asked if he was ever told about the deed by anyone at the Trump Organization, Birney replied, "I don't believe I was." Instead, he said he first learned about it during an "interview with the attorney general's office."

Court then adjourned for the day, with Birney's testimony scheduled to resume tomorrow morning.