For what it is worth, there was a Learjet that was missing for years in New Hampshire, USA. No ELT, it crashed in a remote area and it was finally found by a hunter who just stumbled over it. There was no question of a cover-up, it was just that they could not find one small aircraft that could have been anywhere in a large wooded area using a visual search.
I seem to remember wild rumours that this aircraft had not crashed but had been flown out of Nigeria, just for one. Well, they found it and they found three bodies when there were supposed to be three occupants so that settles that, at least.
I am sorry but if it's a crash that doesn't cause a lot of casualties and seems to be fairly obvious (light aircraft in bad weather in hilly terrain trying a visual approach so probable CFIT) then there's not much reason to put in a lot of expensive effort on an exhaustive investigation. That might not be what the next-of-kin want to hear but it's the truth.
What is the point of making such a fuss here? Do you think there's something mysterious that is worth further investigation? If so, why not come out with whatever theory you have, rather than just fulminating about "Nigeria." The place has so many much bigger problems that one crashed King Air must be low priority. Even in the States I can tell you that such an accident wouldn't get much attention, although, yes, they should be able to do a DNA analysis of the remains. That said, that part really has nothing to do with the air crash per se, does it?
I remember a similar crash in the States when, once they had found the aircraft they just looked at the swathe it cut through the trees, said, "Yup, looks like ol' Earl done screwed up on his home-made NDB approach to his home field," marked the wreckage with big red Xs, took the bodies down the mountain to be buried and that was about all. It can be open-and-shut sometimes.