It's interesting that so many seem to think that the grand jury ruling in the Wilson case is the final word. It's not.
And we're not even talking about a federal, civil rights case. Wilson can still be indicted under Missouri state law. All you need is a second grand jury.
The Fifth Amendment prohibition against double jeopardy does not apply ("attach" in legal parlance) until a case has been tried before a trial jury. Therefore, a prosecutor can simply seek a new indictment from another grand jury.
If people start demanding this, perhaps Wilson won't be off the hook.