As the Manhattan district attorney’s office steps up the criminal investigation of Donald J. Trump, it has reached outside its ranks to enlist a prominent former federal prosecutor to help scrutinize financial dealings at the former president’s company, according to several people with knowledge of the matter.
The former prosecutor, Mark F. Pomerantz, has deep experience investigating and defending white-collar and organized crime cases, bolstering the team under District Attorney Cyrus R. Vance Jr. that is examining Mr. Trump and his family business, the Trump Organization.
The investigation by Mr. Vance, a Democrat, is focused on possible tax and bank-related fraud, including whether the Trump Organization misled its lenders or local tax authorities about the value of his properties to obtain loans and tax benefits, the people with knowledge of the matter said, requesting anonymity because of the sensitive nature of the investigation. Mr. Trump has maintained he did nothing improper and has long railed against the inquiry, calling it a politically motivated “witch hunt.”
In recent months, Mr. Vance’s office has broadened the long-running investigation to include an array of financial transactions and Trump properties — including Trump Tower on Fifth Avenue in Manhattan, various Trump hotels and the Seven Springs estate in Westchester County — as prosecutors await a ruling from the United States Supreme Court that could give them access to Mr. Trump’s tax returns.
The prosecutors have also interviewed a number of witnesses and have issued more than a dozen new subpoenas, including to one of Mr. Trump’s top lenders, Ladder Capital, the people with knowledge of the matter said.
In addition, investigators subpoenaed a company hired by Mr. Trump’s other main lender, Deutsche Bank, to assess the value of certain Trump properties, one of the people with knowledge of the previously unreported subpoenas said.
Months earlier, Mr. Vance’s office had subpoenaed records from Deutsche Bank itself, The New York Times previously reported. More recently, Deutsche Bank employees provided testimony to Mr. Vance’s office about the bank’s relationship with the Trump Organization, a person briefed on the matter said.
Still, despite the burst of investigative activity, prosecutors have said the tax returns and other financial records are vital to their inquiry — and the Supreme Court has delayed a final decision for months.
Manhattan prosecutors have also subpoenaed the Trump Organization for records related to tax deductions on millions of dollars in consulting fees, some of which appear to have gone to the former president’s daughter Ivanka Trump.
The Trump Organization turned over some of those records last month, though the prosecutors have questioned whether the company has fully responded to the subpoena, the people with knowledge of the matter said.
Mr. Trump won an acquittal in his second impeachment trial last week, but remains the focus of at least two state criminal investigations. Besides the inquiry in Manhattan, prosecutors in Georgia are scrutinizing Mr. Trump’s effort to persuade local officials to undo the election results there. His departure from office has left him without the shield from indictment that the presidency provided.
The Manhattan district attorney’s office has not accused Mr. Trump of wrongdoing and it remains unclear whether Mr. Vance, whose term ends in January, will ultimately bring charges against Mr. Trump or any Trump Organization employees.
The Trump Organization declined to comment, but in the past, lawyers for the company have said that its practices complied with the law and have called the investigation a “fishing expedition.”
Mr. Pomerantz, 69, was sworn in earlier this month to serve as a special assistant district attorney, according to Danny Frost, a spokesman for the district attorney, who otherwise declined to comment on the inquiry. Mr. Pomerantz will work solely on the Trump investigation.
The hiring of an outsider is a highly unusual move for a prosecutor’s office, but the two-and-a-half-year investigation of the former president and his family business is unusually complex. And Mr. Vance, whose office has had a few missteps in other white-collar cases, had already hired FTI, a large consulting company, to help analyze Mr. Trump’s financial records.
Prosecutors are scrutinizing whether the Trump Organization artificially inflated the value of some of his signature properties to obtain the best possible loans, while simultaneously lowballing the property values to reduce property taxes, the people with knowledge of the matter said. The prosecutors are also looking at the Trump Organization’s statements to insurance companies about the value of various assets.
The Trump Organization’s lawyers are likely to argue to prosecutors that it could not have duped sophisticated financial institutions that did their own analysis of Mr. Trump’s properties without relying on what Mr. Trump’s company told them. The company’s lawyers are also likely to emphasize that the practice of providing such differing valuations is widespread in New York’s real estate industry.
Deutsche Bank has said it is cooperating with the investigation. A spokesman for Ladder Capital, which securitized the loans years ago and thus no longer owns them, declined to comment.
Mr. Pomerantz, who has been helping with the case informally for months, has taken a temporary leave from the law firm Paul Weiss to join Mr. Vance’s office. Among other tasks, he will likely handle interactions with key witnesses.
Mr. Vance also retained veteran constitutional lawyers to work on the briefs filed in the 18-month legal battle over the office’s subpoena for Mr. Trump’s tax returns and other financial records, which has twice reached the U.S. Supreme Court. The case was argued by Mr. Vance’s general counsel, Carey Dunne, who is helping to lead the investigation.
The court could rule for a second time on the matter soon, potentially putting eight years of Mr. Trump’s personal and corporate tax records and other documents in the hands of prosecutors for the first time, a development that Mr. Vance’s office has called central to its investigation.
Mr. Pomerantz, a leading figure in the New York legal circles, clerked for Judge Edward Weinfeld in Manhattan and Justice Potter Stewart on the Supreme Court. He then became a federal prosecutor in the United States attorney’s office in Manhattan, where he rose to lead the appellate unit before leaving in 1982.
In private practice, he developed a specialty in organized crime and was involved in a 1988 case that helped determine the legal definition of racketeering. His former law partner, Ronald P. Fischetti, estimated they tried nearly 25 cases that involved organized crime in some form or another.
Mr. Pomerantz returned to the Manhattan U.S. attorney’s office to head the criminal division between 1997 and 1999, overseeing major securities fraud and organized crime cases, perhaps most prominently against John A. Gotti, the Gambino boss.
He later joined Paul Weiss, one of the best-known law firms in New York, where he defended Robert Torricelli, the New Jersey senator accused of campaign finance violations.
“He worked both sides of the street, so he’s not going to be biased by virtue of temperament,” said Robert S. Litt, a former general counsel for the Director of National Intelligence, who has known Mr. Pomerantz since 1976.
David Enrich contributed reporting.