Well the limitations of war crimes as defined by the ICC are pretty specific and I can't say I've seen the brief. One of the important limitations is that the breaches must be "part of a plan or policy or as part of a large-scale commission of such crimes" rather than isolated instances.

I don't think however there is much question that the invasion itself was illegal. Only the UN Security Council has the right to organise interventions of member states.

Preferably those involved should have no perceived vested interest either. To a degree, I actually opposed the use of Australian troops in Timor Leste on those grounds and I can certainly see what many Indonesians were not terribly keen on that either. If time was permitting I would have probably preferred a peace-keeping force of Swedes, Bolivians, Canadians and Algerians!