WASHINGTON -- Bryan Pagliano, the State Department IT staffer who helped set up and maintain Hillary Clinton's private email server in her Chappaqua, N.Y. home in 2009, has been granted immunity by the Justice Department, CBS News confirmed Tuesday. Pagliano is cooperating with the FBI in its investigation.

The FBI obtained Pagliano's cooperation, the Washington Post first reported, citing a senior law enforcement official. The Post also suggested that granting immunity to Pagliano is a sign "the FBI investigation into possible criminal wrongdoing is progressing." Pagliano was paid separately by the Clintons to set up the server before he was hired by the State Department.

FBI Director James Comey told a congressional hearing recently that he is "closely involved" in the investigation into Clinton's use of a private email server while she was Secretary of State.

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CBS News confirmed in August that the bureau was investigating whether Clinton or her aides mishandled classified information during her tenure as secretary of state, in relation to her use of the private server. Specifically, the FBI has been trying to figure out how many classified emails Clinton had on her server, and whether the system exposed classified information.

Clinton spokesman Brian Fallon told the Post in a statement that the campaign was "pleased" that Pagliano had decided to cooperate with the FBI, after he had previously invoked his Fifth Amendment privileges when subpoenaed by Congress.

Separate from the FBI investigation, the State Department had been clearing and releasing some 52,000 Clinton emails in monthly batches since last May and finally finished releasing the emails Monday. The campaign and the State Department have said repeatedly that none of the material was marked classified when it it was sent.

CBS News' Pat Milton contributed to this report.