The fact that the police chief has now said that Wilson will likely not be charged shows the police overall have a strong bias against a fair outcome of the grand jury hearing. The chief is in charge.
No, if the grand jury doesn't hand down an indictment, there's no reason to have a trial. It would be a waste of time.
Yes, but why not wait to see what the decision of the grand jury is instead of trying to influence it like the chief is doing.