S1·E6 I Like Matches

A judo practitioner, Yasuda, is prosecuted for stabbing and killing an off-duty patrol officer. Kuryu senses that something is fishy since it doesn't make sense for someone with a high rank in judo to carry a knife around. The president of a loan shark ring, Mr. Otagawa, is then arrested by the chief police after Yasuda admits that he is only following orders to turn himself in. How can Kuryu prove that Mr. Otagawa is responsible for the murder and not Yasuda?