well yeah i know that was a sarcastic post unless you're implying i missed something else
All officer involved shootings are investigated by internal affairs or some federal agency. If internal affairs suspects or detects something wrong they will prove it in court. They will prove if with evidence which can be a witness testimony, an autopsy, defensive/offensive wounds on Brown or the officer, video/audio evidence, dna/forensic evidence, inconsistent police reports, inconsistent officer testimony, evidence of prejudice, etc.
Now should Darren Wilson be arrested? He should be if there evidence pointing to his guilt. As far as I know he is innocent until proven guilty. Only courts, investigators, and government can prove that, the media can't. The only goal the media has is to sell their side of the story that they want people to believe for entertainment and political value.