What relation prosecutors have to the Dutch Safety Board?
They receive the information from the Board. Unfiltered, contrary to the public. Otherwise they should be completely independent. Findings of the board can not be used as evidence in court.
I wonder why Westerbeke is open to the possibility that the source of the high energy objects was something other than a ground to air missile.
Because there is no clear evidence? It is good practice to be open to other possibilities unless one scenario is confirmed by clear evidence. It should be fairly obvious that it has been a missile, but you can not rule out an air-to-air missile yet.
25 metal objects recovered from bodies and luggage.
That should allow to finally proof which type of missile was used. I wonder whether the dutch get samples of a BUK from Russia/Ukraine for comparison...
500 foreign objects were found, but the focus was on 25 of them.
Probably most shrapnell looks quite the same, it is a small amount of fragments that are very unique for each type of missile, so it makes sense to concentrate on those.