Ah yes, the classic 'bad cop/good cop' act – first threaten him with being sealed away and then make him feel sympathetic by taking him to the crime scene. Not much of a choice, though, MC would naturally agree to work with them.
My only wish is that he'd try to look for ways to betray them and escape, but so much for that – just look at how they try to justify their actions: "Oh look, I'm a cute girl that cares about poor kids! How dare you refuse to cooperate with our righteous police, you evil box!"