Zhang finds one obvious clue, which leads to two different people, but the true killer should be one person. He also finds a hidden clue that points to the same person. The clue is that the murderer drank alcohol before the murder. The dried stain on the spit means he drank that night. Zhang thinks that this is the most obvious clue he found in the case. He thinks that the minister of justice should have searched his home to find the evidence, but instead he did not search his home. The hidden clue he finds is the same, as the minister's assumption. The murderer attacked and drowned lian ma while he was in the bedroom, but he didn't realize that he was being watched. He was afraid someone would find out about his secret and never allowed the laundry lady in his room. The laundry lady must have known about this, because he was born poor and had been working as a householder in the east lake for five years.