Story highlights The FBI has done at least one interview with Pagliano and under the cooperation agreement, he may be asked to do more interviews

linton has said she set up the private system for convenience, in order to avoid carrying more than one mobile device to access government and private emails

Washington (CNN) Bryan Pagliano, the former State Department staffer who helped set up Hillary Clinton's private email server, began his cooperation with the FBI and the Justice Department under an immunity deal late last year after initially rebuffing investigators, according to a U.S. law enforcement official.

The FBI has done at least one interview with him, and under the cooperation agreement, he may be asked to do more interviews, the official said.

While he has turned over documents to the FBI related to his management of the Clinton server, investigators sought to interview him because they believed he could shed light on the period during which the server was set up and any discussions with Clinton and her aides about the security for a system that would be storing sensitive government information, according to the official.

Clinton has said she set up the private system for convenience, in order to avoid carrying more than one mobile device to access government and private emails.

Pagliano's attorney would not comment to CNN.

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