<span>Photograph: Jim Bourg/Reuters</span>
Photograph: Jim Bourg/Reuters

Donald Trump's lawyer Christina Bobb was instructed to certify to the justice department that all sensitive government documents stored at his Mar-a-Lago resort had been returned.

The certification of subpoena compliance appears to be at the center of a criminal investigation into obstruction of justice surrounding the former US president after the FBI searched the property and found more than 100 classified documents.

Donald Trump is trying to get back two folders that were taken from Mar-a-Lago.

The saga around the Mar-a-Lago documents has become increasingly fraught in the courts as Trump claims the FBI search is politically motivated. Democrats and the justice department have portrayed the taking of the documents as a national security risk.

The sources said that Bobb received the certification before the counterintelligence chief arrived to collect the records.

Bobb was unsure if the subpoena had been fully complied with, so he told Corcoran to amend the certification to say that all documents responsive to the subpoena would be returned after a thorough search, according to sources.

It wasn't clear why Bobb was willing to sign the declaration when she didn't fulfill her role as the custodian of records.

It wasn't clear why he didn't sign the certification, as well as whether he had asked for Bobb's signature

One of the sources said that Bobb testified to the justice department about the 3 June episode on Friday. Bobb testified for NBC News.

As the justice department conducts a criminal investigation into possible violations of the Espionage Act, obstruction of justice and the retention of government records, the situation surrounding the subpoena certification has become of special interest.

Federal prosecutors alleged in an August court filing that attempts were made to obstruct the government's investigation.

The previously unreported details behind the certification, which were accepted as sufficient by the justice department on 3 June, could change the dynamics of the obstruction investigation if she was misled.

In a motion to the US appeals court for the 11th circuit, prosecutors wrote that Trump's lawyers could be witnesses to relevant events.

The person did not reply to the request for comment. Bobb has told associates since the FBI searched the property that the certification she signed was not true, according to sources.

Bobb could speak more freely if he signed the statement as a custodian instead of a lawyer.