In his court filing regarding the seizure of materials from his Florida resort, Donald Trump appeared to concede that he unlawfully retained official government documents, as the former president argued that some of the documents seized by the FBI could be subject to executive privilege.

The former president’s lawyers argued on Monday that a court should appoint a “special master” to separate out and determine what materials the Justice Department can review as evidence due to privilege issues.

However, Trump’s claim that some of the documents are protected by executive privilege suggests that they are official records that he is not authorized to keep and should have been turned over to the National Archives at the end of the administration.

In that regard, the motion appeared to admit that Trump violated one of the criminal statutes listed on the warrant used by the FBI to search the former president’s Mar-a-Lago resort – 18 USC 2071 – relating to the unlawful removal of government records.

“If he’s admitting to having documents that would have any colorable claim of executive privilege, those are by definition presidential records and belong at the National Archives,” said Asha Rangappa, a former FBI agent and Yale Law School associate dean.

Trump can still argue that a special master be appointed to review the seized documents, obtain a more detailed receipt for what the FBI retrieved from Mar-a-Lago, and prevent the Justice Department from further reviewing the materials until the process is completed.

Former US attorneys argue that there may be communications seized by the FBI that are privileged but not used in furtherance of a crime, and that the justice department should be barred from using them in its investigation. A person directly involved in Trump’s legal defense noted – repeating parts of the filing – that the Presidential Records Act lacked an enforcement mechanism, even as they admitted that the Justice Department might pursue the privilege argument as a tacit admission.

However, Trump’s motion could pose new challenges for the former president, with additional passages in the filing laying out the Justice Department’s months-long battle to recover certain records in a pattern of interactions that could be construed as obstruction of justice.

The search warrant for Mar-a-Lago listed obstruction for the statutes potentially violated, but it was unclear whether this was obstruction of the investigation into the retrieval of government documents from Mar-a-Lago or obstruction of another, separate investigation.

Nonetheless, the section of Trump’s motion titled “President Donald J Trump’s Voluntary Assistance” detailed the numerous steps the justice department took to retrieve 15 boxes in January, additional materials in June, and then 26 boxes when the FBI conducted its search.

The filing discussed how Trump returned the 15 boxes to the National Archives and then “accepted service of a grand jury subpoena” for additional documents with classification markings one day after the National Archives informed Trump’s lawyers that those boxes contained classified documents.

Despite taking custody of documents responsive to the subpoena, the Justice Department learned that there may have been additional classified documents, and issued a subpoena on 22 June demanding security camera footage of the hallway outside where the materials were being stored.

That subpoena for security tapes, as well as a subsequent subpoena for CCTV footage of that area from just before the FBI search on August 8, indicate that the Justice Department did not believe Trump was being completely truthful or forthcoming in his interactions with the investigation.

When the government retrieved materials from Mar-a-Lago for the second time in June, Trump’s custodian of records attested that they had returned documents responsive to the subpoena – only for the FBI to retrieve more boxes of classified materials.

Aside from the late filing of the motion two weeks after the FBI search, the brief appears to be procedurally problematic.

The motion was not filed in West Palm Beach, Florida, where the warrant was approved. Instead, it was filed in Ft Pierce, where the judge has no knowledge of the underlying affidavit – and could rule in such a way to reveal to Trump if he or his lawyers are suspects for obstruction.