Soon after Hillary Clinton's arrival at the State Department in 2009, officials in the information technology office were baffled when told that a young technician would join them as a political appointee, newly disclosed emails show.

The technician, Bryan Pagliano, was running the off-grid email server that Clinton had him set up in her New York home for her work as secretary of state. But even as years passed, Pagliano's supervisors never learned of his most sensitive task, according to the department and one of his former colleagues.

Pagliano's immediate supervisors did not know the private server even existed until it was revealed in news reports last year, the colleague said, requesting anonymity because of a department ban on unauthorized interviews.