Let's extend your hypothetical-- let's stipulate there is a bloodthirsty monster that holds an entire hotel hostage while actively bombing and attacking a nearby town. The monster is de facto hotel manager, because the the despairing people in the hotel at some point elected the the monster to rule the hotel. The sheriff of the town next door (which is being bombed) shows up and defends the town as best they can by attacking the hotel, and there ensues a pitched battle.
What role at that point do bewigged stateless jurists play who have no force of arms at their disposal to defend or attack or secure the peace? As a matter of history Germany did suffer mightily in WWII for the crimes of the Nazis; if the ICC were in operation then would it have arrested (or investigated and hobbled) Churchill, Zukov, Patton and Eisenhower? And then impotently and cynically declared its dissatisfaction with Hitler and Goebbels after blunting the Allies' efforts solve the problem the only practical way available to anyone, by force of arms?
I sympathize with the humanitarian concerns on both sides, but in this case the ICC is demonstrating its own flaws, which are legion. In your hypothetical, the only people threatened by the bewigged jurists are the sheriff and town precisely because they respect the international order and rule of law, and the ICC would, practically speaking, due to its inherent flaws, solely do the bidding of a monster.