First of all give you the pesame by the death of your son. I'm sorry.
About you problem I can't help you. I was in Congo flying in 2007 and DRC civil aviation can't do a investigation as a normal country.
Bukavu is a dangerous airport I was flying in Bravo Air Congo and in two months Bravo had 3 minor incidents and one peasant killed.
Also Bukavu is in a troubled area, "men of the war" want to dominate mineral traffic so "why not think that was shut down?
Is very easy recognize a UN airplane, all white with big black letter "UN".
I can't undertand that no body want to discover what happened. Conspiration? a CVR distroyed? Beech as manufacturer does'nt want discover what happened, and the airline? Very extrange.
Good Luck, I hope you can discover the true in memory of your son.