Investigators are looking at invoking an exception that can bypass attorney-client privilege if legal advice is used for furthering crime.

Federal prosecutors involved in the criminal investigation of Donald Trump’s retention of classified documents argued to a US judge on Thursday that one of the former US president’s lawyers should answer more questions before a grand jury over objections of attorney-client privilege.

US prosecutors have been seeking to invoke the so-called crime-fraud exception that allows them to compel testimony about communications between an attorney and a client when they have evidence to suggest legal advice was used in furtherance of a crime.

In the sealed hearing before the chief US district judge for the District of Columbia Beryl Howell, prosecutors argued that they had reason to believe that legal advice to Trump from his lawyer Evan Corcoran was used by Trump to obstruct the classified-marked documents investigation.

The development is the latest incident in the ongoing saga around Trump’s retention of classified documents at his Mar-a-Lago Florida resort related to his time as president. The papers were discovered after an FBI search of the property amid accusations that Trump was seeking to obstruct an investigation into how and why the documents ended up there.

Subsequent investigations have also turned up documents at properties linked to Trump’s vice-president, Mike Pence, and the Democratic president Joe Biden, relating to his time as vice-president to Barack Obama.

The prosecutors in Trump’s case broadly cited to Howell the same evidence it included in the affidavit used to obtain the warrant to search Mar-a-Lago, sources familiar with the matter said, which alleged potential retention of national security material and obstruction of justice.

Howell did not rule on Thursday on whether to grant the justice department’s motion to compel testimony from Corcoran, the sources said, after Corcoran previously appeared before the grand jury and declined to answer some questions on the basis of attorney-client privilege.

A spokesperson for the justice department and a lawyer for Corcoran did not immediately respond to a request for comment.

The obstruction part of the Trump documents investigation is centered on Trump’s incomplete compliance with a subpoena in May that demanded the return of any classified-marked documents in his possession, after documents he earlier returned to the National Archives included 200 that were classified.

In June, Corcoran searched Mar-a-Lago and produced about 30 documents with classified markings to the justice department and had another Trump lawyer, Christina Bobb, sign a certification that attested to compliance with the subpoena “based on the information provided to me”.

But the justice department, according to court filings, developed evidence that more classified-marked documents remained at the resort, as well as “evidence of obstruction”. And when the FBI searched Mar-a-Lago, they found 101 such documents in a storage room and in Trump’s office.

Corcoran is among three Trump lawyers connected to the documents case who have recently appeared before the federal grand jury in Washington, the Guardian previously reported, in addition to Bobb and one of Trump’s civil lawyers, Alina Habba, who searched Trump’s office in an unrelated case.

The deferment by Howell could mean that she ultimately does not rule on the matter. Howell is slated to step down as chief judge on 16 March and will be succeeded by US district court judge James Boasberg, who previously oversaw the secret foreign surveillance court.