thats quite shocking , and quite brave of you to follow the stolen car like that, however, police should've been informed during the chase (however, when involving the police, thanx to our legal system, one also fears that the police will do nothing but to include you as a "suspect" and indulge you into this whole process as a felony) these fears stops many of us in our daily routine to stop, or at least inform about a crime even if they know its happening
sadly!