"In connection with an unrelated case, the FBI has learned of the existence of emails that appear pertinent to the investigation," Comey wrote the chairmen. "I am writing to inform you that the investigative team briefed me on this yesterday, and I agreed that the FBI should take appropriate investigative steps designed to allow investigators to review these emails to determine whether they contain classified information, as well as to assess their importance to our investigation."
http://www.cnn.com/2016/10/28/politics/fbi-reviewing-new-emails-in-clinton-probe-director-tells-senate-judiciary-committee/index.html
http://www.nbcnews.com/news/us-news/fbi-re-open-investigation-clinton-email-server-n674631