Hallo Johan,
My sincere condolences, even a year later, it is always a terrible loss!!
Due to various reasons , Governments, Companies and some individuals would prefer not to find out the truth.
If I could suggest, normally the most important people who try and establish what happened will be the insurance company who did the insurance of the aircraft.
The reason is: they are the people who have to settle all the insurance claims, that might arrise from an accident. Insurance companies investigate independedly, and some investigators are very good.
My experience with these companies are that they normally investigate all avenues before they make a payment. ( They have there reasons)
Try and establish whith which insurance company the aircraft was insured, who was the investigator, and ask for assistance.
I trust this might help you.