That's what occurred to me immediately reading the article too - there's an excellent chance that they know who it is already. The other shocking thing was that it took at least two or three people to perpetrate.
As someone who has driven from Canberra to Sydney and Canberra to Adelaide on many occasions, the locations of the bodies, in opposite directions immediately made me think of Canberra as a relevant point.
Belanglo Forest was an obvious spot given the Milat murders. One more body might be taken as another unidentified Milat victim (although the police probably have good records of which areas have already been searched on previous occasions).
The SA site is between the Mildura area and Tailem Bend. I go through Balranald and Ouyen myself, but it looks as though the bodies were intentionally dumped in opposite directions from Canberra to reduce the likelihood of the two being connected...