Not long after federal prosecutors issued a subpoena last year for all the classified documents that former President Donald J. Trump took with him from the White House to his estate in southern Florida, one of his lawyers told him, in no uncertain terms, that it would be a crime if he did not comply with the demand, according to a person familiar with the matter.
The lawyer, Jennifer Little, this year related the account of her discussion with Mr. Trump to a grand jury overseen by the special counsel Jack Smith. She is one of several witnesses who prosecutors were told had advised Mr. Trump to cooperate.
A few months after Ms. Little testified to the grand jury, Mr. Smith charged Mr. Trump with violating the subpoena for the documents and obstructing the government’s repeated efforts to reclaim nearly three dozen classified documents that he removed from the White House.
As part of her grand jury appearance, Ms. Little told prosecutors that the former president clearly understood her warning, the person familiar with the matter said.
Her sworn testimony that Mr. Trump was aware that disregarding the subpoena would be a criminal offense could serve as significant evidence of his consciousness of guilt if she ends up being called as a witness when the case eventually goes in front of a jury.
The details of her testimony were reported earlier by ABC News.
The remarks by Ms. Little, who was already working for Mr. Trump in connection with a criminal investigation in Georgia and was brought in to help advise him on how to comply with the subpoena because she was one of the few people around him who knew the criminal justice system, were made during a critical meeting in the spring of 2022. At Mar-a-Lago, Mr. Trump’s private club and residence in Florida, she and another lawyer, M. Evan Corcoran, advised the former president that he needed to obey the government’s demands that he return the classified material.
The indictment filed by Mr. Smith in June accuses Mr. Trump of illegally holding on to 32 classified national security documents and then conspiring to cover up his actions with two of his aides at Mar-a-Lago. The case is set to go to trial in Federal District Court in Fort Pierce, Fla., at the end of May.
While Mr. Corcoran has received outsize attention in the case — largely because Mr. Smith’s team managed to get a court order to obtain the audio notes of his discussions with Mr. Trump — Ms. Little has so far maintained a lower profile.
It was unclear what else Ms. Little testified to in her grand jury appearance.
On Wednesday night, Steven Cheung, a Trump campaign spokesman, denounced “misleading leaks” about the case that showed “utter disregard” for attorney-client privilege.
“President Trump has consistently been fully cooperative, and told the key D.O.J. official, in person, ‘Anything you need from us, just let us know,’” he said.
Ms. Little was initially subpoenaed to appear before the grand jury, in Federal District Court in Washington, on Jan. 25. Both she and Mr. Corcoran initially tried to avoid providing testimony, arguing that their dealings with Mr. Trump were protected by attorney-client privilege.
But in March, Judge Beryl A. Howell, who was then Washington’s chief federal judge, forced both of them to appear before the grand jury under what is known as the crime-fraud exception. That provision allows prosecutors to work around attorney-client privilege when they have reason to believe that legal advice or legal services have been used in furthering a crime.
Several aides to Mr. Trump told him that he had to comply with the subpoena for the classified documents, which was issued to him in May 2022. According to Mr. Smith’s indictment, Mr. Trump asked Mr. Corcoran what would happen if he did not cooperate with federal prosecutors.
“What happens if we just don’t respond at all or don’t play ball with them?” the indictment quotes him as saying.
Ms. Little stopped being directly involved in the documents case not long after that meeting, according to two people familiar with the matter, but she remains involved with Mr. Trump.
She is currently helping to represent him in a criminal case in Fulton County, Ga., where he stands accused of state charges of seeking to overturn the results of the 2020 election.
