Comey's letter to Congress announced the discovery of 1,000 (UPDATE: make that tens of thousands) new, potentially relevant, emails (some of which may be duplicates of those already in the FBI's possession) discovered in an unrelated investigation. While Comey didn't mention which investigation, FBI sources reportedly confirmed that the new emails were discovered on devices belonging to Anthony Weiner, husband of Killary's top aide Human Abedin.
After several years of scandals where Weiner engaged in 'sexting' (and god knows what else) with various women, Weiner and Abedin separated in August after it was revealed that Weiner had, yet again, sent lewd texts to a woman, including a picture of himself with an erection while lying in bed with his young son.
On September 21 this year, Weiner was again exposed (literally and figuratively) when the British Daily Mail published an article claiming that Weiner exchanged sexually-themed text messages with a 15-year-old girl from North Carolina. (Huma and Hillary sure have great taste in men!).
The American Thinker reports:
It was announced ten days ago that grand jury would be convened to investigate Weiner's sexting "by the end of the month." The timing of Comey's letter strongly suggests that the devices containing new emails were obtained through a grand jury subpoena, with no immunity deals or evidence destruction needed. If that is the case, further subpoenas are quite possible, a tool that was left unused in the investigation to date.