The FBI investigation swirling around Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE’s presidential run appears to have entered its final stages.

Many of the former secretary of State’s top aides have been interviewed over the course of the last month, and Clinton herself is expected to answer investigators’ questions about her use of a private email server in the coming days or weeks.

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Former officials and legal experts say the Democratic front-runner's testimony will likely be the final puzzle piece for federal prosecutors and FBI investigators as they decide whether to file any charges over her use of a personal email server while secretary of State.

“This certainly sends the signal that they are nearing an end to their investigation,” said Steven Levin, a former federal prosecutor and current partner at the law firm Levin & Curlett.

Though FBI officials have said Clinton is not the target of the probe, they would want to be as prepared as possible before going in to interview her, Levin said.

“Typically, the way we structured investigations when I was a federal prosecutor is that we would seek to interview the target last,” he said.

“As you begin to interview people who are extremely close to the target of an investigation — people who are considered confidants … you typically interview those people towards the final stages of the investigation,” he added. “So that way if they tell you something that is contrary to something you’ve already learned, you can immediately challenge them on that information.”

The end of the investigation would be a relief for Clinton and her allies, who have faced questions for months over her exclusive use of the personal server.

Though her rival in the Democratic primary, Sen. Bernie Sanders Bernie SandersKenosha will be a good bellwether in 2020 Biden's fiscal program: What is the likely market impact? McConnell accuses Democrats of sowing division by 'downplaying progress' on election security MORE (I-Vt.), has vehemently refused to attack her over the email issue, Republicans are sure to use it against her in the general election.

For Clinton, the stakes of the final interview will be high.

“There’s a lot of jeopardy that is going to happen in this interview. It’s very high-stakes,” said Matthew Whitaker, a former U.S. attorney who now leads a watchdog group called the Foundation for Accountability and Civic Trust.

The trick for Clinton, he said, will be to make sure that her story lines up with the testimony provided by her aides.

“They’re only going to ask her questions that they know the answers to already,” he said.

Attorney General Loretta Lynch and FBI Director James Comey have both denied that they are seeking to wrap up the investigation by this summer’s presidential conventions, or by any other point on the political calendar.

But the bureau’s accelerated pace suggests it is well aware of the ticking clock of the campaign season; many doubt that the case would drag on for much longer without a resolution of some sort.

If prosecutors wanted to press ahead with an indictment, they may have their work cut out for them.

In Clinton’s case, none of the more than 2,000 emails now considered classified on her system were marked as such at the time they were sent, complicating the question of whether she or her allies broke the law.

“Was this simply a sloppy handling of documents, or was it knowing and intentional mishandling of classified information?” asked Barry Pollack, a lawyer at Miller & Chevalier who previously defended convicted CIA leaker Jeffrey Sterling.

Since none of the documents were marked as classified at the time, Pollack said, prosecutors would either need to find a clear pattern of Clinton or her aides sending emails with obviously sensitive information, or else prove that the system was created to circumvent existing rules.

Multiple media outlets have reported federal officials have yet to find any evidence that Clinton intended to violate the law.

Still, that might not necessarily get her off the hook from some misdemeanor charges, according to national security lawyer Bradley Moss.

“[T]he extent to which the person intended to remove classified documents is irrelevant,” he said in an email to The Hill. “All that matters for strict legal purposes of culpability is whether the person, by virtue of their official position, came into possession of classified information and affirmatively removed the information to an unauthorized location (i.e., the private server).

“Whether the person knew or suspected the information was classified is irrelevant.”

Other legal experts questioned the claim, hinting at the legal minefield that could await any potential criminal case.

The FBI did not respond to an inquiry about the investigation. A spokesman with the U.S. Attorney for the Eastern District of Virginia, which is reportedly assisting in the case, declined to comment.

In addition to the interviews, federal investigators will have reams of files to go through.

It remains unclear whether officials have managed to recover any of the roughly 30,000 emails Clinton deleted from her machine, which she claimed were personal. If they did, the messages could provide a treasure trove of information.

Bryan Pagliano, the IT specialist believed to have helped set up and maintained Clinton’s server, was granted immunity in exchange for his help with the investigation.

Whatever the outcome of the case, the political controversy over Clinton’s email setup is unlikely to subside.

Even if the Justice Department comes up empty, Freedom of Information Act (FOIA) lawsuits are currently making their way through the courts and are likely to shed additional light on Clinton’s setup for months to come.

Over the next two months, at least six current or former aides to Clinton will be asked to give depositions as part of those cases, which are being led by the conservative watchdog group Judicial Watch. Clinton herself could be asked to testify as well, a federal judge has ruled.

“Out litigation’s going to continue,” Judicial Watch president Tom Fitton told The Hill in a recent interview.

“It doesn’t really matter what the FBI does, what the Justice Department does, in the sense that we have an independent right to get some accountability and to have the FOIA law vindicated.”

Republicans, for their part, show no signs of letting up.

“Hillary Clinton’s reckless attempt to skirt government transparency laws with her secret email server jeopardized our national security by exposing classified information on more than two thousand occasions,” Republican National Committee Chairman Reince Priebus said in a statement on Friday.

“Clinton’s irresponsible behavior as secretary of State and her deliberate attempts to mislead the American people show she lacks the judgment and character to be president.”