Madison says that no man is allowed to be a judge in his own case, bc his interest would bias him. why is that? someone me.

Madison says that no man is allowed to be a judge in his own case because his interest would bias him. This is definitely true. Okay lets say Joe robs a bank. He gets caught and he has court the next day. If Joe was the judge he would give his reasoning of why he did it, and say he isnt guilty of theft therefore he is released. Im not sure how to give an example and this is the best i could come up with, 

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