There is actually a whole article on their murder, quite extensively detailing the days leading up to their death as the days that follow it (not in English though): https://nl.wikipedia.org/wiki/Moord_op_de_gebroeders_De_Witt

To me, the most disturbing part is the next sentence:

The brothers were shot and then left to the mob. Their naked, mutilated bodies were strung up on the nearby public gibbet, while the Orangist mob ate their roasted livers in a cannibalistic frenzy. Throughout it all, a remarkable discipline was maintained by the mob, according to contemporary observers, lending doubt as to the spontaneity of the event.

How the fuck do you eat people’s liver in a frenzy but disciplinedly?? That makes no sense, right? Please tell me it’s not possible.