Unfortunately, the ATSB are no longer at arm's length from CASA.
It wasn't that long ago that the ATSB had no qualms identifying any perceived failings when investigating an accident - including CASA failings. It used to be that they'd look at all the holes in the Swiss cheese, however as of at least the Pelair accident at Norfolk Island, they only really looked at the last piece of cheese i.e. the pilot in that accident and as a result, ATSB credibility has been shot to pieces. To my mind, this is due to the personalities & (cosy?) relationships that exist at high levels within CASA/ATSB/Government...
As stated above, the fact that CASA didn't supply requested/required information as part of an investigation & that this apparently was not pursued appropriately,only reinforces this viewpoint...