The National Archives discovered more than 700 pages of classified documents in 15 boxes recovered from Donald Trump’s Mar-a-Lago home in January, a letter between the National Archivist and Trump’s legal team shows. The May 10 letter also said that among the classified material was “special access program materials,” which are among the most closely guarded secrets in the U.S. government. The explosive letter was published late Monday by John Solomon, a conservative journalist and one of Trump’s authorized liaisons to the National Archives for reviewing documents from his time in the White House. The message also showed that both the National Archives and federal investigators had become deeply worried about the national-security lapse caused by secret documents being kept at Trump’s Florida estate, as well as the former president’s resistance to share the documents with the FBI. National Archivist Debra Wall also indicates in the correspondence that she rejected Trump’s claim to privilege over the documents due to national-security concerns relating to the classified material.