Interviews with the lender, Deutsche Bank, and the insurance broker, Aon, are part of an ongoing criminal investigation into the president and his company, The Trump Organization, which will continue after he leaves office next month. The interviews were first reported by The New York Times.
As part of the same investigation, the district attorney's office has sought via subpoena eight years' worth of Trump's personal and business tax returns. The president has fought the subpoena for more than a year, and the two sides are waiting to see whether the U.S. Supreme Court will, for the second time, take up the matter.
A member of Trump's legal team told ABC News on Friday that the subpoena amounts to an illegal "fishing expedition" and declined to comment further.
The president has also argued, so far unsuccessfully, that he is immune from any aspect of criminal prosecution while in office -- but those asserted protections end in January. Any potential self-pardon President Trump may be considering would not apply should Manhattan District Attorney Cy Vance decide to bring charges.
Vance's office declined to comment on the case or its pursuit of any potential witnesses.
Deutsche Bank and Aon -- which are not thought to be accused of any wrongdoing in their association with The Trump Organization -- have signaled they are cooperating with the inquiry. Their employees could help Vance's investigators understand how the president's company valued certain assets as it pursued loans or tax benefits.
A source familiar with matter told ABC News that Deutsche Bank would not have loaned Trump money without doing its due diligence.
Nonetheless, the bank has reportedly been examining ways sever ties with Trump after he leaves office. Trump's company owes the bank an estimated $340 million, according to filings to the U.S. Office of Government Ethics in July. Sen. Elizabeth Warren, D-Mass., has called for an investigation into Deutsche Bank and has demanded answers about its relationship with Trump.
The president's former lawyer, Michael Cohen, who has pleaded guilty to lying to Congress and campaign finance violations, testified in 2019 that his former boss inflated or deflated his net worth as it suited his business needs.
Hush payments Cohen said he arranged to women who alleged long-denied affairs with Trump are also part of the district attorney's investigation.