As cited by CNBC, NBC's Pete Williams provides some much needed color, and says there doesn't appear to be that anyone intentionally withheld evidence or emails in the Clinton investigation; they found new emails after coming across a device in the course of an unrelated investigation and while looking at that device, that's what led them to the new emails. Williams adds that this is not coming out after Russian hacking or from the Podesta leaks.
In other words, the FBI is now probing what is on the device and what are the emails on it.
Which brings up a valid question, as asked by the Washington's Examiner's Tim Carney: "what was the "unrelated investigation" that turned up new HRC emails. Any chance it was about taxpayer-backed export finance?
NEW: In course of an unrelated investigation, FBI came across a device & they were led to new emails mentioned in today's letter to CapHill pic.twitter.com/BE4WJiwP9h— CNBC Now (@CNBCnow) October 28, 2016
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However the details pan out, it is troubling for Hillary that 10 days before the election, the FBI's probe has been effectively reopened.