Why should it be illegal if they are law enforcement?
There's no exemption in the law that allows agents of other governments to compromise .us systems.
We don't go after the thousands of hacks that occur on a daily basis yet you want to single out police by doing it for a good cause?
You know, that's a fair point. My intention wasn't to say that I think they should be singled out, but rather that what they did should be considered a criminal act, and that their being Australian LEO is completely irrelevant to whether or not charges are brought. I don't think we should encourage or tolerate some wild west mentality where if you have a badge in country A, it's OK to ignore the laws of every other country on the planet. You're right, though, that there are a lot of crimes that occur on a daily basis that we don't prosecute because they're not the biggest fish to fry.
Just to reiterate, though, I don't think giving someone a hyperlink that doesn't do anything other than display the content they asked for constitutes hacking anyway.