Umineko's versions of the Knox rules are slightly different, but you've got the idea.
A Chinaman refers to a character whose motivations are incomprehensible; mystery novels those days would use culprits from the 'mysterious Orient', and who knows how those weirdos think, right? Nowadays you might think of criminals who are criminals because they are criminals; it's like that.
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"As the size of an explosion increases, the number of social situations it is incapable of solving approaches zero." -Vaarsuvius, Order of the Stick