Why do certain cases go to the grand jury (e.g., Ferguson) and others don't?

The main factor is what state the case occurs in. Only 25 states use grand juries with any regularity, and only 22 states require them. And of the 22 states that require them, there are differences in which crimes they require them for. So in New York, everyone charged with a felony has the right to demand an indictment from the grand jury (though they can waive this right). In Minnesota, meanwhile, the grand jury is used almost exclusively for indicting homicide suspects. And in California, the grand jury is mostly used to investigate the government.

(See here for an overview of how grand juries are used in the US and some of the differences between various state practices.)

Grand juries determine whether enough evidence exists for a case to go forward to a criminal trial, either before a jury or a judge. By law, they operate in secret and hear only evidence presented by prosecutors, who also instruct the grand jurors on the law. Defense lawyers are barred from speaking. For a decision, 12 jurors who have heard all of the evidence must agree.

I’m going to skip the topic of Eric Garner and the video that did not sway the grand jury.

However, I am going to point out some powerful reasons why many US lawyers believe Grand Juries are generally used to exonerate police in cases of aggressive force.

Grand Juries depend on police testimony to make cases and therefore might be tempted to sandbag indictment proceedings where they are perhaps against police officers.

On top of that, Ferguson DA Robert P. McCulloch had a father who was a police officer who was killed in the line of duty when he was 12. He is also president of an organization that donates money to families of police/firefighters/EMTs killed in the line of duty, an organization that was selling t-shirts that helped fund the defense for (former) Officer Darren Wilson.

Any juror in the juror pool of a typical criminal or civic trial who had admitted to any of these characteristics would have easily been dismissed in voir dire, but somehow the prosecutor need not recuse himself?

In a case like this, even if the grand jury outcome was correct, the fact that this DA did not recuse himself is going to forever leave open the question, rightly or wrongly, that he sandbagged this either consciously or unconsciously.

If we can’t even get this part right (recusing someone with a conflict of interest) in such a high profile case, what the hell is happening in the cases going on across this country every day?

Thank you, @SavoirFaire and @geeky_mama.

Jurisdictions operate differently