The FBI is reopening the investigation into Hillary Clinton's email server, multiple sources are reporting.

NBC News, as well as Congressman Jason Chaffetz, are reporting that FBI Director James Comey has sent a letter to Congress saying that the investigation into Clinton's server is now open to re-examine additional emails for classified information. These additional emails were discovered during an unrelated investigation. ( It is unknown at the time as to what this "unrelated" investigation concerns . EDIT: The investigation concerned Anthony Weiner's sexts to an underage girl.)

FBI Dir just informed me, "The FBI has learned of the existence of emails that appear to be pertinent to the investigation." Case reopened — Jason Chaffetz (@jasoninthehouse) October 28, 2016

NBC News: FBI re-opening investigation into Hillary Clinton’s private e-mail server — Jesse Rodriguez (@JesseRodriguez) October 28, 2016

And the actual letter:

BIG: The FBI is reopening its investigation into @HillaryClinton's email server. Here's the letter from the FBI to Congress: pic.twitter.com/OKjipTeiJp — Frank Thorp V (@frankthorp) October 28, 2016

This post has been updated.

Earlier, this post had an update that said the investigation would be completed in two to three days. This is incorrect and came from a now-deleted tweet from WaPo's Erik Wemple. There is no timeline for the investigation as of yet.