Sadly as far as the political big picture is concerned it probably doesn't really matter who the OEM of the MANPAD really is/was when you take into account who is carrying out the investigation.
Even if it is of Russian or Chinese origin I really wouldn't be surprised to see the investigation coming back with a US or NATO origin as that is most likely to fit the required political agenda.
Someone is probably searching the shelves for enough bits to back the story already.
I say Chinese because IMHO everything that NK does is done following a quiet nod/request from their neighbours.