FBI Director James Comey’s announcement Friday that his agency would revisit the probe into Hillary Clinton’s handling of classified material immediately raised new questions about what evidence agents may have missed in the year they had already spent investigating the case.

In a letter to members of Congress, Comey said an “unrelated case” led agents to additional Clinton emails that may contain classified information. A congressional aide told the Washington Examiner the letter came to members completely “out of the blue” on Friday.