So some government officials were probably in the pocket of Halliburton (i.e., just like the US government) while selling a weak justification to the public.
Such things play a part, of course, however at a nation level the first order consideration would have been ANZUS like defence agreements and a sense that ongoing regional support from the US rested on Australian support for the US, right or wrong.
This. Whether the USA had a mandate to go into Iraq wouldn't have been questioned. Australia jumped in because we always jumps in to whatever bullshit war the USA dreams up. For some reason we see it as an obligation to support our allies in all their wars, even when we think their reasons are ridiculous and even when we know they won't support us in return.
This has lead to serious problems in the case of the Afghan war, where it was clear that this whole conflict had nothing to do with Australia, could not even vaguely be construed as "defence", achieved nothing, cost Australian lives, and was a completely fabricated mess that we got into for really bad reasons (I paraphrase). The SAS war crimes thing was a symptom of our unease at our involvement (imho) - we would not normally question the things that soldiers do in conflict, this was more a way of questioning why we were in the conflict in the first place.
Been ongoing for a while now: https://roncobb.net/img/cartoons/aus/k5092-on-Tucker_Box-cuu...