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Manhattan prosecutors are getting frustrated with Trump Organization CFO Allen Weisselberg and his lack of cooperation with their investigation into the company, a person familiar with the matter told The Washington Post on Monday.

Weisselberg, 73, is the most senior executive at the Trump Organization who isn't a member of the Trump family. Prosecutors are looking into whether he paid taxes on benefits he received from former President Donald Trump, including leased cars and apartments, the Post reports. The hope has been that he would feel the squeeze and cooperate with a separate investigation into the Trump Organization and whether the company committed financial fraud by manipulating property values to get loans and tax benefits. 

Former Trump Organization employees say Weisselberg plays a key role in the company and knows everything about its finances and taxes. He signs most checks and keeps a close eye on all expenses, and "to just say 'he's the money man' actually underestimates his role," Tristan Snell, the lead on the New York attorney general's completed investigation into Trump University, told the Post. "He was more than that even. He was the whole enchilada. Allen Weisselberg really ran the whole company."

Weisselberg continues to go into work at Trump Tower, and has been in the building when Trump is visiting. It's believed he's still regularly communicating with Trump, the Post reports, and by going into the office, he could be trying to show that he remains loyal and is rebuffing the prosecutors. A grand jury convened by Manhattan District Attorney Cyrus Vance Jr. is expected to decide whether to indict Trump. 

So far, Weisselberg and Trump have not been accused of any wrongdoing, but if prosecutors can prove the Trump Organization did misrepresent its assets to a bank, tax authorities, or insurers, this could be a legal disaster for Weisselberg, the Post says. Robert C. Gottlieb, a defense attorney and former prosecutor, told the Post he believes Weisselberg is "playing Russian roulette with the district attorney's office if he thinks that even if he is indicted he is going to get a pass. We're not talking about fraud involving a few thousand dollars, we're talking about allegations of a massive fraud involving millions of dollars over an extended period of time in which he as CFO."