The Philippine Senate has witnessed political coups, scandals and the occasional shouting match.

It had never, until this week, seen a sitting senator sprint down its corridors in a muddy olive shirt, knocking aside female investigators like bowling pins, to avoid an international arrest warrant for crimes against humanity.

That was Monday. By Wednesday night, gunshots were ringing out in the building that houses the upper chamber of the country’s Congress.

“I worked in the Senate for 15 years and I have never seen anything like this,” said Dr Jean Franco, a political-science professor at the University of the Philippines. She was not alone in that assessment.

At the centre of the turmoil was Senator Ronald “Bato” dela Rosa, a former national police chief who helped oversee ex-president Rodrigo Duterte’s war on drugs, and a man who once dismissed the deaths of children in that bloody campaign as “collateral damage”.