If you have evidence, call Australia polices. I believe in Australia polices and the judicial system.
If you do not have evidence, it is just your speculation. If you do not believe the fairness of Australia polices, protest against them.
Your initial message ended with "Speaking louder in public place is not breaking any LAW." This indicates that you were responding to some claim that the counter-protesters had broken a law by being louder in public. I haven't seen any claims resembling that so I'm curious to see where you did.