Why does he need to get involved?
He will give his statement to the authorities in an official capacity but he is not necessarily going to help matters by talking about it openly. The legal teams at Arsenal and any other official organisations, that are going to dealing with the matter, will have more than likely told him not to comment on it in too much detail otherwise it runs the risk of muddying the waters, weakening the case, etc.
That is my opinion, of course, if what was said was racially motivated then it is going to be an extremely sensitive and emotional case, Arteta does right just standing back and answering any questions with generic answers or not answering at all.