Multiple witnesses subpoenaed in Florida in Trump Mar-a-Lago case | Donald Trump

Federal prosecutors have subpoenaed multiple witnesses to testify before a previously unknown grand jury in Florida in the criminal investigation into Donald Trump’s handling of national security materials and obstruction of justice, according to people familiar with the matter.

The new grand jury activity at the US district court in Miami marks the latest twist in the investigation that for months has involved a grand jury that had been taking evidence in the case in Washington but has been silent since the start of last month.

Trump aide Taylor Budowich is scheduled to testify before the Florida grand jury on Wednesday, one of the people said, and questioning is expected to be led by Jay Bratt, the justice department’s counterintelligence chief detailed to the special counsel Jack Smith, who is leading the investigation.

The previously unreported involvement of Bratt could suggest the questioning could focus on potential Espionage Act violations, particularly whether Trump showed off national security documents to people at his Mar-a-Lago resort – a recent focus of the investigation.

Bratt, who was seen arriving in Miami on Tuesday by this Guardian reporter, has previously appeared for grand jury proceedings in the espionage side of the investigation, as opposed to the obstruction side, which has typically been led by Smith’s other prosecutors or national security trial attorneys.

A justice department spokesperson declined to comment.

But the underlying reasons as to why prosecutors in the special counsel’s office impaneled the new grand jury in Florida, and whether it is now the only grand jury active in the case after the Washington grand jury has sat dormant for weeks, remains an open question.

Prosecutors would most probably prefer to bring charges in Washington, where the judges at the US district court are more familiar with handling national security case – though Florida also has a robust national security section – and the jury pool skews more Democratic.

The impaneling of grand juries has to do with where prosecutors believe a crime was committed. And the most straightforward reason for the Florida grand jury is that prosecutors have developed evidence of criminal activity at Mar-a-Lago, which is in the southern district of Florida.

In this investigation, prosecutors considering charges against Trump for retaining national security material may have concluded from the evidence that he was still president when classified documents were moved to Mar-a-Lago, meaning his “unlawful possession” only started in Florida.

Similarly, if prosecutors have also developed evidence that Trump knew he had retained national security documents after he left office at Mar-a-Lago, for instance by waving them around or showing people, that could present hurdles to charging espionage act violations in Washington.

The venue for an obstruction of justice charge is more difficult to deduce, meanwhile, because the courts have provided little guidance about how it should be applied under section 1519 of the US criminal code, which prosecutors listed on the affidavit for Mar-a-Lago search warrant.

Generally, other obstruction statutes hold that the venue depends on where the impeded proceeding was taking place. In the Trump documents investigation, the subpoena last year demanding the return of classified documents was issued in Washington.

The US court of appeals for the DC circuit, however, has ruled in previous cases that the correct venue is where acts of obstruction took place. If prosecutors are considering obstruction charges for Trump’s steps to conceal classified documents after the subpoena, Florida could be the venue.

Separate to the question of why prosecutors impaneled a new grand jury in Florida is what it indicates in terms of the status of the criminal investigation.

If both the Florida grand jury and the Washington grand jury are active, that could indicate prosecutors are considering charges in both places and against the same targets. But if the Florida grand jury is the only grand jury in operation, that could suggest several things. It could be that the investigation in Washington is largely finished, and prosecutors have finalized whether to charge Trump and others there, but are still weighing separate charges in Florida.

Or prosecutors might have concluded charges in Washington and are at risk of dismissal over improper venue because the crimes occurred at Mar-a-Lago, and are moving the entire case to Florida.

Moving the entire case to Florida would not necessarily be that burdensome for the special counsel, legal experts said, and would just involve prosecutors reading out transcripts of testimony previously delivered to the Washington grand jury, in addition to questioning new witnesses.

For months, prosecutors have examined whether the failure by Trump to fully comply with a subpoena demanding the return of any classified documents was a deliberate act of obstruction, according to multiple people with knowledge of the case.

Last June, the since-recused Trump lawyer Evan Corcoran found 38 classified documents in the storage room at Mar-a-Lago and told the justice department that no further materials remained there – which came into question when the FBI seized 101 additional classified documents months later.

Corcoran later told associates he felt misled because he had asked whether he should search elsewhere at Mar-a-Lago, like Trump’s office, but was waved off, the Guardian first reported. Corcoran’s notes also showed he told Trump he had to return all classified documents in his possession.

The investigation has also been focused on whether Trump showed off national security materials at his other properties like the Trump Bedminster golf club in New Jersey, including a document concerning military action against Iran, people close to the case said.

Prosecutors have seemingly been trying to identify whether that Iran document was the same document Trump referenced on an audio recording in which he said he could not discuss it because he did not declassify it while in office – though he should have, the Guardian previously reported.

To that end, prosecutors have showed an Iran document to some witnesses who appeared before the Washington grand jury and asked whether they had ever seen the material by Trump or anyone else. It was not clear whether any witness confirmed seeing the document, one of the people said.