WASHINGTON — The Justice Department has granted immunity to the former State Department staffer who worked on Hillary Clinton's private email server, as part of a criminal investigation into the possible mishandling of classified information, according to a senior law enforcement official.
The official said the FBI had secured the cooperation of Bryan Pagliano, who worked on Clinton's 2008 presidential campaign before setting up the server in her New York home in 2009.
As the FBI looks to wrap up its investigation in the coming months, agents will likely want to interview Clinton and her senior aides about the decision to use a private server, how it was set up, and whether any of the participants knew they were sending classified information in emails, current and former officials said.
The inquiry comes against a sensitive political backdrop in which Clinton is the favorite to secure the Democratic nomination for the presidency.
So far, there is no indication that prosecutors have convened a grand jury in the email investigation to subpoena testimony or documents, which would require the participation of a U.S. attorney's office.
Spokesmen at the FBI and Justice Department would not discuss the investigation. Pagliano's lawyer also declined to comment.
In a statement, Brian Fallon, a spokesman for the Clinton campaign, said: "As we have said since last summer, Secretary Clinton has been cooperating with the Department of Justice's security inquiry, including offering in August to meet with them to assist their efforts if needed."
He also said that the campaign is "pleased" that Pagliano, who invoked his Fifth Amendment rights before a congressional panel in September, is now cooperating with prosecutors. The campaign had encouraged Pagliano to testify before Congress.
As part of the inquiry, law enforcement officials will look at the potential damage had the classified information in the emails been exposed. The Clinton campaign has described the probe as a security review. But current and former officials in the FBI and at the Justice Department have said investigators are trying to determine whether a crime was committed.
Clinton has apologized for what had happened: "Yes, I should have used two email addresses, one for personal matters and one for my work at the State Department. Not doing so was a mistake. I'm sorry about it, and I take full responsibility."
Any decision to charge someone would involve Attorney General Loretta E. Lynch, who told Congress when asked earlier this month about the email inquiry: "That matter is being handled by career independent law enforcement agents, FBI agents, as well as the career independent attorneys in the Department of Justice. They follow the evidence, they look at the law and they'll make a recommendation to me when the time is appropriate.
"We will review all the facts and all the evidence and come to an independent conclusion as how to best handle it," she added.
Current and former officials said the conviction of retired four-star general and CIA director David H. Petraeus for mishandling classified information is casting a shadow over the email investigation.
The officials said they think that Petraeus' actions were more egregious than those of Clinton and her aides since he lied to the FBI, and classified information he shared with his biographer contained top secret code words, identities of covert officers, war strategy and intelligence capabilities. Prosecutors initially threatened to charge him with three felonies, including conspiracy, violating the Espionage Act and lying to the FBI. But after negotiations, Petraeus pleaded guilty to a misdemeanor charge of mishandling classified information.
He was fined $100,000 and sentenced to two years of probation. FBI officials were angered by the deal and predicted it would affect the outcome of other cases involving classified information.
The State Department has been analyzing the contents of Clinton's correspondence, as it has prepared 52,000 pages of Clinton's emails for public release in batches, a process that began in May and concluded Monday. The State Department has said 2,093 of Clinton's released emails were redacted in all or part because they contained classified material, the vast majority of them rated "confidential," the lowest level of sensitivity in the classification system.
Clinton and the State Department have said that none of the material was marked classified at the time it was sent. However, it is the responsibility of individual government officials to properly handle sensitive material.
The email investigation is being conducted by FBI counterintelligence agents and supervised by the Justice Department's National Security Division.