I agree with Ansett and Austman. I did not read the '400 passengers' remark as a generalised one: it was referring to this particular flight, which was operated by a QF A330 that seats 30 passengers in business and 267 in economy class.
This capacity of 297 is a long way short of the '400' quoted. I'd bet that the flight wasn't full, which means an even lower number of actual passengers. Exaggeration rarely helps to build an intellectual case.
If the AFP cannot get basic facts and figures obtainable from a quick Internet search correct, how good will its work that requires detailed investigation be?
Like jso, I worry that the cost of these 'air policemen' must be huge. While they no longer fly domestically, there is only a tiny number of incidents on international flights ex Australia. From memory, the marshals do not fly on all international carriers into and out of Australia, only Australian-domiciled ones, but I am happy to be corrected on that point.
With plane coughpit doors reinforced and normally locked, there seems little need for taxpayers to bear the huge cost of transporting these 'sky marshals' (an American term I dislike) around the globe.
This is the sort of public policy that is more based on 'being seen to do something' rather than 'being effective.'
I'd much prefer that we spent this sort of money on building infrastructure: a new fast train along Oz's east coast to reduce the need for inefficient air travel, new rail and road links in cities and so on. Of course, infrastructure isn't cheap, but my point is that governments are inclined to waste money on ineffectively employing people rather than on providing the infrastructure that actual enables small businesses to create jobs.
Don't, however, get me started on how on the ground airport security is a giant job creation scheme.
IATA has latterly acknowledged that airport security needs to change. It's inefficient, costly, lacks a risk-based approach and can be unnecessarily intrusive to those who are well behaved travellers simply wanting to get from A to B:
Technology will eliminate intrusive airport security searches, says IATA boss - Business - The Guardian