Brick's opening sequence

We know that this is an opening sequence because it has many close ups which do not show all of what is going on. Also, it is quite confusing, as an opening sequence only really "opens" the film up to make you sit down and watch the rest. We also know that it is an opening sequence (of a thriller) as it shows the last part, first. (A dead girl lying in a waterway, then going back to when she was alive, giving a note that sais the place name of where to meet her, to a boy).