Mr. Cipollone and Mr. Philbin are the most senior officials who worked for Mr. Trump who are known to have been interviewed by investigators after the National Archives referred the matter to the Justice Department this year. Mr. Philbin was interviewed in the spring, according to two of the people familiar with the matter, as investigators reached out to members of Mr. Trump’s circle to learn how 15 boxes of material — some of it classified as classified — they got on their way. at his Mar-a-Lago resort in Palm Beach, Florida. It was not clear when he interviewed Mr. Cipollone. Mr. Cipollone and Mr. Philbin were Mr. Trump’s representatives to deal with the National Archives. were named to the positions shortly before the president’s term ends in January 2021. At some point, after National Archives officials realized they lacked Trump White House documents required to be preserved under the Presidential Records Act, they contacted Mr. Philbin for help in their return. A spokesman for Mr. Philbin did not immediately respond to a request for comment. Mr. Philbin has tried to help the National Archives retrieve the material, two of the people familiar with the discussions said. But the former president repeatedly resisted the pleas of his advisers. “It’s not theirs, it’s mine,” several advisers say Mr. Trump told them. The former president returned 15 boxes of material to the National Archives in January, but the Justice Department issued a subpoena in May for documents still at his residence. On June 3, counterintelligence officials with the Justice Department’s national security division went to Mar-a-Lago to collect the remaining classified documents. At that point, at least one Trump lawyer signed a statement saying material with the classified markings had been returned, according to four people familiar with the document. But officials then used a subpoena to obtain surveillance video of the hallway outside a warehouse at Mar-a-Lago and saw something that worried them. They also received information from at least one witness who reported that more material may remain at the residence, people familiar with the investigation said. Mr. Philbin is among eight people who currently or have worked for Mr. Trump contacted by the FBI since a grand jury was empaneled this year. Investigators also interviewed Derek Lyons, former White House staff secretary. Mr. Lyons’ last day in the White House was Dec. 18, 2020, meaning he did not know how the last boxes were filled as Mr. Trump prepared to leave. But he did have information about the flow of paper in the White House and how the former president handled the material. The FBI has contacted about half a dozen people who currently work for Mr. Trump and who may know what documents he may still have in his possession.