I mean how many cases are there? Is it only 4 cases in the game?
Oh, you mean the scenes. Forgot I called them "cases" in the gallery. There are actually 5, as counted by the gallery, yes. Refer to this to check if you've seen everything. Note that that's more than 5, since it's listing smaller things that aren't full scenes in the gallery. But if there's something there that doesn't sound familiar, that's probably the missing bit.