In 2016 hackers hit a whole bunch of Yahoo accounts. One of those Yahoo accounts happened to he Huma Abedin.
What the hackers had found is that Huma had been forwarding classified emails from State to her Yahoo and then storing them on the laptop she shared with Weiner.
Weiner got busted for sexting a 15 year old and part of the warrants that were issued were to review his laptop he shared with Huma. The NYPD officers that found THE HRC emails were shocked to find them on that laptop.
HRC emails were not the only thing they found on that laptop, they also found Child porn. Child porn so brutal that the officers/investigators who viewed them had to go to therapy.
NYPD did not have faith that the NYO FBI would act thoroughly on this case because of the election and to protect those who were also involved with the Clintons.