I saw a documentary about this not long ago....IIRC, blame was put on the kid flying the plane; likely got disoriented.
Yes, the investigators concluded that spatial disorientation was the cause. The pilot was not instrument rated, but took off into deteriorating instrument conditions. There was also heavy icing reported in the area, but it is unlikely that played a significant roll because the flight was so short. Since the wreckage wasn't discovered until the next morning, though, there is no way to know conclusively whether or not icing added to the situation.