Sad fact is as I see it a BOI is set up for one reason and one reason only, to find the truth as to what happened to help prevent it happening again and possibly save some poor soul losing their lives........ When politics get into it and higher ranked officers attempt to alter the findings for what ever reasoning that lesson is lost, the pressure to come to a set finding, even if the incorrect one simply buries the truth and leaves the possibility of it happening again, that is why the Civil AIB works so well, it is independent from the airlines or manufacturers etc and works to find the truth.
Additionally they and I don't mean this badly a service board are simply not someone placed in a position that they are not 100% qualified to judge on, such as proffessional accident investigators.... You wouldn't if getting court marshalled take the court appointment officer to defend you (if you had any sense) you would use a proffessional lawyer.... The same should cover BOI's it needs an independent and qualified inspector.