Donald Trump’s retention of classified-marked documents at his Mar-a-Lago resort is distinguished in the eyes of the justice department from that of Joe Biden or Mike Pence as a result of one particularly crucial difference: suspected obstruction of justice.

Legal experts believe the situation for the former US president is more perilous than others swept up in the scandal because of his reluctance to cooperate at key moments in the investigation and his unwillingness to proactively search his properties for marked documents after becoming aware that he possessed such papers.

The justice department has added in court filings that it suspected Trump of concealing classified-marked documents at Mar-a-Lago – and while that might be the most aggressive characterization, the trouble for Trump is that he has handled his case far differently from Biden and Pence.

The recent discoveries of marked documents, first at Biden’s office in Washington and home in Delaware, and then at Pence’s home in Indiana, reflect how presidential transitions are chaotic and senior government officials are clearly unaware of the contents of boxes packed by aides.

But what matters to the justice department – and what distinguishes an inadvertent error from a potential crime – is what happens once classified-marked documents are found and whether officials take steps to ensure they have returned any such papers to the government.

“If they found Trump took them away, purposely, but then as soon as the archives said he had, he said: ‘Oops, sorry, here have them back,’ I don’t think they would be considering charges,” former US attorney Harry Litman said of the criminal investigation into Trump.

To date, Biden and Pence freely gave up the marked documents as soon as they were found and proactively allowed their lawyers to search their properties out of an abundance of caution – whereas the department found getting documents back from Trump to be a monumental struggle.

Trump’s legal team has suggested the first time they knew of classified-marked documents in the former president’s possession was when they were issued a grand jury subpoena on 11 May, demanding the return by 24 May of any marked papers, regardless of whether they had been declassified.

Trump’s lawyer Evan Corcoran asked for a roughly two-week extension to comply with the subpoena, which the justice department initially declined, before giving him a one-week extension until 7 June. Corcoran then told the department they could collect documents on 3 June.

At Mar-a-Lago, Corcoran returned a folder of documents and, at Trump’s urging, took the officials from the justice department to the storage room that he had searched, and asked them to be in touch if they needed anything more. The Trump lawyers also presented a sworn statement attesting compliance.

Trump’s legal team has said the 3 June meeting was not obstructive, since Corcoran believed, albeit erroneously, that he was in full compliance and Trump went out of his way to show them the storage room that had been searched, and was prepared to let them search it themselves had they asked.

But from the perspective of federal prosecutors, a source familiar with the matter said, the overtures were deceptive: the compliance was incomplete, and the FBI seized 101 classified-marked documents from the property, including from the storage room that they passed off as clear.

“The big element here is that you know they want the documents back and you resist or impair,” Litman said. “That false certification is strong evidence of intent. It’s hard to say: ‘Oh, you wanted them all back, I’m so sorry, we’ve been so busy,’ when they signed that paper.”

The prosecutors, the source said, have not regarded being shown the storage room to be a mitigating factor for an additional reason: the burden to ensure compliance with a grand jury subpoena was not on the justice department and tacitly allowing them to search the room was meaningless.

For Trump’s case to mirror that of Biden or Pence, Trump essentially would have had to comply with the subpoena, but then proactively conduct another search of his resort – as Biden later did with his home – and proactively search his other properties, as Biden did with his beach house.

But as it turned out, once the justice department left Mar-a-Lago that day in June, Trump’s lawyers made no effort to ensure no more classified-documents remained at the resort, or any other property, until the department repeatedly sought them to do so around Thanksgiving – a search that turned up two more marked papers.