A prosecutor has great influence over a grand jury and can direct them where the prosecutor wants to take them. The prosecutor controls who becomes a witness and which pieces of evidence the grand jury sees. First keep in mind that most prosecutors do not like to lose cases in trial. Too many losses can cost a prosecutor his/her position. So the starting point for a prosecutor is analyzing the strength of any given case. If a prosecutor believes it is a good case, or they really want a person indicted, only the evidence of guilt will be brought to the grand jury. If the prosecutor believes it is a weak case, and it will be lost at trial, even if the grand jury indicts, the prosecutor will let the grand jury hear all the evidence which weakens the case and “guide” them to no indictment.
In Ferguson, it appears the prosecutor let the grand jury hear and see all the evidence, pro and con. While this is not regularly done, it is totally legitimate and it gives the appearance of impartiality for the prosecutor.
In Ferguson, I opine there were three critical factors which led to the grand jury’s final decision. The first is that many of the most vocal witnesses against the officer, alleging Mr. Brown was shot in the back, were proven to be lying. Second, is that the majority of witnesses verified that Mr. Brown was leaning into the cruiser where the officer was seated. Third, and most compelling, is that some of Mr. Brown’s blood was found inside the cruiser giving physical proof that Mr. Brown had entered the cabin of the cruiser. This series of 3 factors could easily establish for the grand jury that Mr. Brown was the aggressor. Actually this is very aggressive behavior, which few regular citizens would ever even think about doing. I believe that after the grand jury locked down these factors, the remainder of the “contested events”, since none could be verified one way or another, would fall by the wayside leading to no indictment aka “no true bill”.
Overall the grand jury and trial by jury are part of a very effective, albeit slow, justice system geared towards protecting the innocent. I have tried dozens of felony trials and very few where I believed the jury made a terrible mistake. Actually there was one trial where the defendant was found guilty and I was very upset. When the defendant applied for early release several months later the judge called me to his chambers remembering how upset I was. He then showed me a letter from my client to the judge admitting his guilt. The jury was right and I was wrong. On the other hand, I have had juries acquit my client at trial and then be upset with the prosecutor (they still did not like me) because they felt the prosecutor dropped the ball. They made the proper decision even though they were not happy about it.
You can’t ask much more from a group of ordinary citizens.