Firstly, this is Australia, not the USA. There are no free speech protections and that isn't necessarily wrong - just different.
While I'd defend someone's general right to free speech - as most Australians would - I won't defend it for people expressing things - especially hateful things - anonymously. If you don't have the guts to put your name to what you say and to cop the free speech back, then you don't deserve the right to speak in the first place.
So to the law in question. It was originally written with telephones in mind. It's purpose is to place a big stick over behaviours that are hard to track. The ex who rings their former partner in the middle of the night from a payphone every night for a month, etc.
In the case in point, a women was raped and murdered - a very rare thing in Australia. The mocking of this person no doubt by anonymous hard to track people is not free speech. When there is no face behind the words, it is cowardice wanting to provoke without taking the heat. If a society wants to seek them out and punish those kinds of people, I think they ought to be able to.