OM#401 - Doesn't seem to be much for the ATSB to be involved with.
We can agree, there were a couple of fatalities; this means a Coroner is involved. Insurance and other interested folks are going to look to that Coroner for answers.
The inquest will need to know, to be 'legally safe' (to be sure) exactly what and why. So, the ATSB do the technical stuff which will look at how or why the aircraft crashed and killed. The QPS (bless 'em) do their bit and the CASA do theirs.
The Coroner then has a nice big pile of paperwork to read through, ask questions of; and, make whatever recommendations and rulings are judged to be required.
To get it right, the Coroner needs as close to the whole truth as humanly possible; that means answers: which means full, independent, unbiased investigation by all three agencies. There are lots of question to answer about how things got to a stage where the prang occurred. Preventable, Yes M'lud, I believe it was.