The latest twist in the investigation into former President Donald J. Trump’s handling of classified documents is the surprise revelation that a previously unknown federal grand jury in Florida recently began hearing testimony in the case.

The grand jury in Florida is separate from the one that has been sitting for months in Washington and has been the center of activity for prosecutors as they investigate whether Trump mishandled the classified documents after leaving office or obstructed efforts to recover them. Among those who have appeared before or been subpoenaed by the Washington grand jury in recent months, people familiar with the investigation said, are more than 20 members of Trump’s Secret Service security team.

But there are indications that the Washington grand jury, housed in the city’s federal courthouse, may have stopped hearing witness testimony in recent weeks, according to three people familiar with its operation.

As for the Florida grand jury, which began hearing evidence last month, only a handful of witnesses have testified or are scheduled to appear before it, according to people familiar with its operation. At least one witness has already testified there and another is scheduled to testify on Wednesday.

It is an open question why prosecutors convened the Florida grand jury, which is sitting in US District Court in Miami, and whether it is now the only one hearing testimony. This uncertainty, due in large part to the secretive nature of grand juries, serves to underscore just how much special counsel Jack Smith’s handling of the document case remains out of the public eye.

“We know a small fraction of what agents and prosecutors know, so it is dangerous, if not impossible, to discover government strategy from afar,” said Chuck Rosenberg, a former federal prosecutor and FBI official. “He’s like the guy who berates a referee for missed calls from the cheap seats.”

But despite much being shrouded in mystery, legal experts and people familiar with the investigation suggested there could be any number of reasons why Mr. Smith may have chosen to use a Florida grand jury for at least some elements. of the case. His decision could have significant effects on the development of the investigation.

Put simply, the people familiar with the matter said, if both grand juries are up and running, it suggests prosecutors are considering filing charges in both Washington and Florida. It is possible that Trump could be charged in one jurisdiction while others involved in the case are charged in the other.

But if only the Florida grand jury is currently hearing testimony, it suggests two possibilities.

One is that the investigation in Washington is largely complete and that prosecutors are now ready to make a decision on bringing charges there while they still weigh other potential charges in Florida.

The other is that Mr. Smith has decided that Florida is the right place for any charges he may bring in the case and has moved the entire grand jury there, they said.

(Another possibility is that the Florida grand jury is simply hearing evidence for the convenience of local witnesses, although that option would seem less likely since more than one witness has appeared before it.)

It wouldn’t be all that unusual if Mr. Smith’s team opened the document investigation in Washington and then decided to move it to Florida because of legal issues related to the location, said Brandon L. Van Grack, a former federal prosecutor who worked on cases involving security and classified stuff.

“It’s common in situations involving classified information when prosecutors aren’t sure where to base an investigation in Washington, Virginia or Maryland,” Mr. Van Grack said. “The point is that just because it starts there, doesn’t mean it has to end there. You don’t know what your potential hooks are on the spot until you’ve completed a thorough investigation.”

Mr. Van Grack said it would be relatively easy to move a grand jury investigation from Washington to Miami if necessary. Prosecutors would simply have to read the first grand jury transcripts to new grand jurors or ask federal agents to offer them a summary of the most important points.

If Mr. Smith is considering filing charges in both Washington and Miami, the latter may involve potential targets who live and work in Florida. Investigators, for example, have been examining the functions of two Trump employees at Mar-a-Lago, his private club and residence, for their roles in the storage and security of classified documents there.

Even if the Washington grand jury is now on hiatus, it may be able to reconvene and vote to impeach Trump. If not, however, and only the Florida grand jury remains in operation, that would suggest that Mr. Smith’s office concluded that a case against Mr. Trump or his aides should be based only in Florida, people familiar with. The issue. saying.

There would be reasons for that latter decision, said Timothy Parlatore, a lawyer who resigned from Trump’s legal team last month. Many of the central events of the document investigation took place when Trump lived in Florida, he said.

Trump was residing in Mar-a-Lago when he and his lawyers first began negotiating the return of government records to the National Archives in late 2021. And the initial trove of classified documents the archives uncovered was in a batch of 15 boxes of records that Mr. Trump sent to Washington from Florida.

Florida is where Trump was living when the Justice Department issued his subpoena last May for the return of all classified documents in the possession of his presidential office. And when prosecutors in Washington sought a meeting with Trump’s lawyers to enforce that subpoena and collect any relevant materials, it was held at Mar-a-Lago.

After prosecutors came to believe that Trump was still holding classified material even after the subpoena, they sent the FBI to search Mar-a-Lago. Agents made off with another 100 or more classified documents that were discovered at the Florida compound in violation of the subpoena.

But prosecutors could still seek to establish a Washington venue for charges against Trump, especially since moving a potential case to Miami would not be without risk for Smith and his team.

A Florida jury might prove more sympathetic to Trump than a Washington jury. And judges in the Southern District of Florida, including Aileen M. Cannon, who made the unusual decision to halt the investigation in its early stages so that an outside arbitrator could review the documents seized at Mar-a-Lago, may be more inclined to govern in favor of Trump than those of Washington.

jonathan swan contributed reporting.