Actually:
1. I have no reason to believe the comments attributed to the officer that Mr. Brown looked like a robbery suspect, particularly given the facts about the shooting already appear to contradict what the officer has said about it (location of the body, for example). Also, of course, the officer may never have said this to begin with.
2. Even if the officer was correct about Brown looking like a description of the robbery suspect, the officer has the right to stop and query him (even to arrest him) but he, the officer, has to presume that Mr. Brown is innocent and is so until convicted in a court of law.
3. Even if Mr. Brown was guilty of the robbery (and there is zero evidence of that) then the officer had no right to shoot a fleeing individual. Even a convicted one. The officer only can use deadly force if he believes that his life, or that of another person, is in direct and imminent danger. Even if Ms. Brown wrestled for the gun (and there is some testimony that he did not), once he stopped and ran the officer could not shoot him.
4. I find it interesting that some people are willing to assume certain facts that are at best very weak rumors. I don't know the facts, except Mr. Brown appears to have been quite a distance from the officer when he was shot, that he was shot multiple times, and that he was unarmed. I think most sides agree with these facts. There are some testimonies that he was holding his hands up at the time he was shot, but I am willing to wait to see if that was true, too. But even looking at the agreed on facts, the shooting looks indefensible whatever else might be established. And the subsequent actions by the local police don't enhance my confidence in them.