Former President Donald J. Trump received a subpoena this spring in search of documents that federal investigators believed he had failed to turn over earlier in the year, when he returned boxes of material he had improperly taken with him upon moving out of the White House, three people familiar with the matter said.
The existence of the subpoena helps to flesh out the sequence of events that led to the search of Mr. Trump’s Florida home on Monday by F.B.I. agents seeking classified material they believed might still be there, even after efforts by the National Archives and the Justice Department to ensure that it had been returned.
The subpoena suggests that the Justice Department tried methods short of a search warrant to account for the material before taking the politically explosive step of sending F.B.I. agents unannounced to Mar-a-Lago, Mr. Trump’s home and members-only club.
Two people briefed on the classified documents that investigators believe remained at Mar-a-Lago indicated that they were so sensitive in nature, and related to national security, that the Justice Department had to act.
The subpoena was first disclosed by John Solomon, a conservative journalist who has also been designated by Mr. Trump as one of his representatives to the National Archives.
The existence of the subpoena is being used by allies of Mr. Trump to make a case that the former president and his team were cooperating with the Justice Department in identifying and returning the documents in question and that the search was unjustified.
The Justice Department declined to comment. Christina Bobb, a lawyer working for Mr. Trump, did not respond to messages. It is not clear what precise materials the subpoena sought or what documents the former president might have provided in response.
The subpoena factored into a visit that Jay Bratt, the Justice Department’s top counterintelligence official, made with a small group of other federal officials to Mar-a-Lago weeks later, in early June, one of the people said.