The prosecutor knew that he didn’t have a case, unlike 99% of the Lefties out there, he read the evidence. In a normal case, he would have simply declined to prosecute and not bothered to go to the Grand Jury. Many, many cases are disposed with exactly in this fashion - prosecutors do not waste time, energy, and resources on cases that are going nowhere.
But, he couldn’t do that here, the lynch mob was in full cry. So by doing a document dump to the Grand Jury and letting them sort through it to get to an inevitable conclusion, he bought time, shifted the blame, and put a stamp of citizen review on it all. This is how Grand juries used to operate, but they have not done so for a long time.
The disappointed lynch mob will just have to content themselves with burning down minority owned businesses.