Just doing a blackie and trolling through old news articles on this crash back in '08 and came across this one:
CASA investigating aviation company over fatal crash - ABC Local - Australian Broadcasting Corporation
In particular this paragraph may hold the answers on who investigated??...
A spokesman for the the Australian Transport Safety Bureau (ATSB) says it is not investigating the accident because it is a police matter.
Sorry in advance if this was already stated, but it would appear that the QPS may have investigated this accident..."however I cannot confirm or deny...yada,yada..!"