Presumably the local police or the highway patrol. Presumably, the GBI is not the only law enforcement agency in Georgia, nor would I think they are normally responsible for investigating motor vehicle accidents. The indictment was for vehicular homicide—I.e causing death by reckless driving or violating traffic laws (here, he was charged with following too close).
I doubt the GBI, let alone this specific agent, was in charge of such an investigation. I’ve certainly seen nothing other than rank speculation to support such a motion.
So far, I have seen no connection between the dead GBI agent and Harrison Deal, except that they were two individuals (out of hundreds) who died in Georgia in December 2020.
Fair enough, Sydney gets the benefit of the doubt though. She’s done more to get to the truth, save patriots and take down bad actors than anyone else out there.