Taking a leaf from the Judgment at Nuremberg, "just following orders, don't fly".
The police may say they were merely following orders. Most importantly, the Nuremberg Principles drafted by America and its Allies firmly established that for all nations, whether they became signatories to the Principles or no, there is no excusing of war crimes or crimes against humanity by claims of 'just following orders,' or by virtue of being a government official, or by claims of not knowing that their conduct was a war crime, or of not being capable of stopping such crimes. No such excuses are allowed under international law.
I do hope such principles can also be applied during peace time demonstrations against governments who continuously flout the ethics of good governance. The demonstrators were not terrorists bearing arms to overthrow a government. They just want to march to the Merdeka Stadium. Why couldn't the police allow them that grace? Just following orders? The way the police behaved as though they were on a war footing.