Justice Department officials have granted immunity to the aide who set up Hillary Clinton's private server.
Bryan Pagliano, the former Clinton campaign staffer who maintained the controversial email network, is now cooperating with investigators with the FBI, according to a report Wednesday evening by the Washington Post.
Clinton and her senior aides may soon face questioning from law enforcement agents as they continue their investigation into whether the State Department team mishandled classified information on a network of unsecured cell phones and tablets.
Since June of last year, the State Department has upgraded more than 2,000 emails to a classified level, including 22 emails that were withheld in full because they contained top secret material.
Clinton has denied wrongdoing in the year since her use of a private email server became public. Her campaign continued to characterize the FBI probe as a routine "security review" in response to reports about Pagliano's immunity.
Pagliano invoked his Fifth Amendment rights and refused to answer questions when he was called before the House Select Committee on Benghazi to testify about his role in running the email network.
Clinton's deputy chief of staff, Huma Abedin, is the only other Clinton aide known to have used an email account housed on the private server, which was kept in Clinton's Chappaqua home.
The latest development could complicate Clinton's efforts to put questions about her emails behind her as she closes in on her party's nomination.