Seeing reports that the FBI agent who was in charge of the investigation abruptly resigned. Shocker.
It would be conceivable that Ross, and the other officers present, were interviewed by the FBI.
The FBI presented the interviews and the videos to the Civil Rights Division.
The FBI likely had access to the driver's phone and her partner's phones at this point.
The Civil Rights Division determines, based on the interviews, the videos and the phones, that the officer acted in self-defense, and made the decision that there was no predicate for continuing the investigation into Ross.
An FBI agent then wishing to pursue the investigation, with no authorization from leadership, then would be in a situation where the agent abides by the determination. Or the agent resigns.
And if any new information arises, the investigation may be re-opened.