Rotaryman is wrong. NSW Police- and others of the states and territories in Australia are absolutely permitted to carry their firearm airside of the security screening point. They certainly aren't permitted to carry it on board.
If the copper was carrying his firearm in a briefcase then this is a big red flag to any security screener (worth their money) that the copper is probably intending on traveling. Therefore it would require the question to be asked. We're back to square one. Was the copper asked the question? If not then the training of the screener and/or competency of the screener is inadequate. If the copper was asked the question and lied about it then they're up for a pretty hefty fine in my book.
It'll be interesting to see how this pans out.