The justice department is weighing whether to grant immunity to the Trump adviser Kash Patel and force his testimony about claims that highly sensitive government documents the FBI seized from the former president’s Mar-a-Lago resort were declassified, according to sources familiar with the matter.

The status of the documents has emerged as relevant to the criminal investigation surrounding Trump’s mishandling of national security materials since it could strengthen a potential case that the former president was in violation of state secrecy laws.

Trump and advisers such as Patel have claimed repeatedly since the FBI search in August that the documents bearing classification markings found at the property had in fact been declassified before the former president departed the White House.

The claims that the documents were declassified have not been supported by evidence, however, and Trump’s lawyers have not repeated the assertions in a related legal dispute before a judge or in court filings where they could face penalties for lying.

Justice department officials are examining whether to allow federal prosecutors to seek an order from the chief US district court judge in Washington Beryl Howell granting Patel limited use immunity to compel his testimony on the declassification issue and other matters, the sources said.

The consideration for Patel appears to center on the fact that as one of Trump’s appointed representatives with the National Archives, he could offer material insight into the nature of the documents and how the former president regarded the records.

And as a confidant to Trump with whom he maintains a close personal relationship, Patel appears to be in a position to speak to additional areas of interest in the investigation, including about how the documents came to end up at Mar-a-Lago and how Trump responded to requests for their return.

Patel is an ardent Trump loyalist who started the Trump administration railing against the Russia investigation when he served on the House intelligence committee’s Republican staff and ended it as chief of staff to the defense secretary.

Trump considered installing Patel as deputy CIA director in the weeks after the 2020 election until he was dissuaded by lawyers in the White House counsel’s office. Patel remained at the defense department, which delayed the deployment of the national guard for hours during the Capitol attack.

The justice department is broadly averse to granting immunity – which offers guarantees against prosecution based on testimony or information derived from testimony – since it can potentially make bringing charges against the person in the future more difficult.

The approval must also come from the top echelons of the justice department, according to guidelines, and the preference for prosecutors to obtain testimony is to have defendants plead guilty and then have them offer cooperation for a reduced sentence.

In contemplating granting use immunity to Patel, the justice department would essentially be weighing whether to forgo a case against him in order to secure testimony that could lead to constructing a case against a more significant target such as Trump, a former US attorney said.

The justice department had sought testimony from Patel when he was summoned to testify before a grand jury in Washington hearing evidence about Trump’s potential mishandling of national security materials and obstruction when he appeared resisted requests for their return, one source said.

But Patel asserted his fifth amendment right against self-incrimination to an array of questions at the 13 October appearance, the source said, though the basis for some was not clear; even if the documents were not declassified, making false public statements would probably not be a crime.

In the obstruction investigation surrounding Trump by the former special counsel Robert Mueller, for instance, prosecutors concluded that the former president’s false statements about his campaign’s ties to Russia would only have been criminal if he made them to Congress or the FBI.

That led to the justice department seeking a hearing before Howell, the source said, where prosecutors disputed Patel’s basis for declining to testify – but the chief judge broadly agreed with Patel’s lawyers that he could reasonably believe he had reason to assert the fifth.

A spokesman for the justice department and a lawyer for Patel declined to comment. But it appears to face a tricky decision about how to proceed with Patel, as well as with additional Trump aides and employees who have become caught up in the ongoing criminal investigation.

Prosecutors in recent weeks have attempted to reinterview Trump’s personal valet Walt Nauta, who previously worked as West Wing valet before following the former president to Mar-a-Lago at the end of the administration, the sources said.

The justice department grew skeptical of Nauta’s accounts about how he removed boxes from a storage room at the property where documents marked classified were being stored, after it issued a grand jury subpoena in May for the return of a range of documents.

Nauta’s accounts – as well as testimony about Trump directing him to move boxes from the storage room – changed slightly between interviews, the sources said, leading prosecutors to seek a further interview under the tacit threat of potentially charging him with obstruction.

That shadow of potential prosecution has alarmed Nauta, according to a source directly familiar with the matter, and he appears to have so far declined to be interviewed on the advice of his lawyer, who coincidentally also represents Patel.