Flashback: Allen Weisselberg told reporter that he had seemingly lost $1 billion of Trump's money

Longtime Trump Organization CFO Allen Weisselberg will be testifying this week at a criminal trial alleging that the Trump Organization engaged in fraudulent financial activities.

But as Bloomberg's Tim O'Brien notes on Twitter, there have been indications that the Trump Organization has engaged in shady financial practices for decades now.

O'Brien was sued by Trump in 2006 when he published a book called "TrumpNation: The Art of Being the Donald" in which he claimed that Trump massively overinflated his net worth.

While doing research for the book, he talked with Weisselberg after Trump asked him to give a rundown of his net worth, which he claimed at the time was up to $6 billion.

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However, it didn't take long for O'Brien to start puncturing holes in the Trump Organization's façade.

"To put my confusion to rest [Trump] then told Weisselberg to tally the value of all of his assets, net of debt, and discuss them with me," O'Brien explained in a column written four years ago. "Weisselberg, reading from a large notepad, told me that Trump’s holdings were worth about $6 billion. But after I added up Weisselberg’s valuations, the total only came to $5 billion."

O'Brien then asked the Trump Organization CFO if he could account for the seemingly missing $1 billion, which is a substantive amount of cash to have lost.

“I’m going to go to my office and find that other billion," Weisselberg told him, although he never got back to O'Brien to reveal if he'd found it.