Manhattan prosecutors investigating former President Donald J. Trump and the Trump Organization have cited the personal banking records of the company’s chief financial officer, questioning gifts he and his family received from Mr. Trump.

Over the past few weeks, prosecutors have trained their focus on the executive Allen H. Weisselberg in what appears to be a determined effort to win his collaboration. Accused of no wrongdoing, Mr Weisselberg has overseen the Trump organization’s finances for decades and could hold the key to a possible criminal case in New York against the former president and his family business.

Manhattan District Attorney Cyrus R. Vance Jr. is investigating, among other things, whether Mr. Trump and the company falsely tampered with property values ​​for credit and tax breaks.

It is unclear whether Mr. Weisselberg would cooperate with the investigation and neither his attorney, Mary E. Mulligan, nor Mr. Vance’s office would comment. However, should a review of his personal finances reveal possible misconduct, prosecutors could use this information to urge Mr. Weisselberg to take them through the inner workings of the company. The 73-year-old accountant began his career with Mr. Trump’s father.

Regardless, prosecutors are demanding a new round of internal documents from the Trump Organization, including ledgers of several of its more than two dozen properties that the company failed to turn over in the past year, according to knowledgeable people. who spoke on condition of anonymity to discuss sensitive details.

The ledgers provide a line-by-line breakdown of each property’s financial health, including daily earnings, checks, and receipts. Prosecutors could compare this information with the information the company provided to its lenders and local tax authorities to determine if it fraudulently misled them.

Mr. Vance’s office has also cited records from several banks that Mr. Trump or his company had accounts with, including JPMorgan Chase and Capital One, according to people with knowledge of subpoenas issued at the banks.

The previously unreported developments underscore the escalation of the investigation after Mr Vance’s office received Mr Trump’s tax filings and other underlying financial documents in February. You were released on Mr. Trump’s objections after a protracted legal battle that culminated in a ruling by the United States Supreme Court.

The Trump organization declined to comment. In the past, Republican Trump has denied any wrongdoing and described the investigation as a longstanding and politically motivated “fishing expedition”. Mr Vance, a Democrat, recently announced that he was not seeking re-election.

The investigation focused on some of Mr. Trump’s best-known properties: the Trump Tower on Fifth Avenue in Manhattan, the Trump Hotels in New York and Chicago, and the Seven Springs Estate in Westchester County. In addition to potential tax and bank fraud, prosecutors are examining statements made by the Trump Organization to insurance companies about the value of various assets.

Prosecutors have cited documents from a company hired by Deutsche Bank, one of the former president’s main lenders, to assess the value of three Trump hotels on Deutsche Bank loans. The company was reviewing the operation of restaurants, bars and gift shops in the hotels, said one respondent.

Last year, prosecutors summoned Deutsche Bank itself and Mr Trump’s other major lender, Ladder Capital, who sold its loans to the Trump Organization years ago. Both banks work together with the prosecutors.

It is unclear whether the prosecution will ultimately bring charges. However, if a case were created against the Trump organization based on the loan records, the company’s lawyers could argue that Deutsche Bank and Ladder Capital are sophisticated financial institutions that have done their own analysis of Mr Trump’s real estate without themselves relying on the company’s internal reviews. The attorneys could also emphasize that it is customary and appropriate in the New York real estate industry to make different valuations of a property depending on the situation – for example, when applying for a loan or when challenging local property taxes – also because there are different methods of calculating Property values.

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If the prosecutor were to indict Mr Trump – far from certain – the outcome would be the potential criminal case against a former president. For his part, Mr. Trump dismissed the investigation as a politically motivated “fishing expedition” and vowed to “keep fighting”.

External accountants also review the information provided to local tax authorities, which may reduce the likelihood of fraud. Mr Trump has argued that his tax returns were “filed by one of the largest and most prestigious law and accounting firms in the United States”.

In addition to the fraud investigation, Mr. Vance’s office remains focused on his original objective: the role of the Trump Organization in paying hush money during the 2016 presidential campaign to two women who said they did business with Mr. Trump.

Former Mr. Trump personal attorney and fixer Michael D. Cohen paid $ 130,000 to buy the silence of one of the women, Stephanie Clifford, the pornographic film actress who appeared as Stormy Daniels. The Trump Organization later made a refund to Mr. Cohen, and Mr. Vance’s office has verified that the company has properly recorded the $ 130,000 payment.

Mr Cohen, who pleaded guilty to collecting federal campaign funding fees in 2018 for his role in the hush-money system, has long implicated Mr Weisselberg, claiming that he helped develop a reimbursement masking strategy. The federal prosecutor who charged Mr. Cohen did not accuse Mr. Weisselberg of wrongdoing.

Mr Cohen is now cooperating with Mr Vance’s investigation and has met with prosecutors several times, including to review some of Mr Trump’s financial documents. Lanny Davis, an attorney for Mr. Cohen, declined to comment.

The prosecutor also questioned Mr. Weisselberg’s former daughter-in-law, Jennifer Weisselberg, she said. Ms. Weisselberg got involved in a bitter divorce from Mr. Weisselberg’s son Barry, who manages the Trump Wollman Rink in Central Park.

Ms. Weisselberg said in an interview that prosecutors asked her about a number of gifts Mr. Trump and his company gave to the Weisselberg family over the years. These include an apartment in Central Park South for Mrs. Weisselberg and her ex-husband, cars rented for several family members, and private schooling.

Examining the gifts appears to be part of an effort to paint a picture of Mr. Weisselberg’s financial life, as is common when prosecutors seek the cooperation of a potential witness. It is unclear whether prosecutors suspect wrongdoing related to the gifts.

James B. Stewart and Steve Eder contributed to the coverage. Susan C. Beachy contributed to the research.