Early Version of Cache?

Haneke's Cache that is. I've seen the movie twice now and there's something unsettling about the last scene. I don't think that Doctor Vorzet (the old one married to the young pretty woman) wrote all (or all but one of the letters as the ending implies). The story of the morphine is the key here and it's only mentioned in passing a few times. Patient 13 was in pain and needed morphine but Marie Corbin was stealing the morphine to assuage Doctor Vorzet's addiction - patient 13 then suicides - something that most likely would not have happened if he had been on morphine. While we don't see a letter referencing this, it's quite likely a letter was sent to patient 13's mother referring to this whole morphine business, so she kills Dr. Vorzet not because she thinks he sent the letter to her son but because she received a letter saying that he prevented morphine from being given to her son. A subtle difference but what it does now is that we don't know who sent _all_ the letters. It appears to me that _everyone_ was getting in on the action of sending letters - not only that but since there is no conclusion, the letters are going to keep appearing after the movie ends. P.S. nice acting by a 15 year old! 9/10