The waiter

Gu Xin came to the table and sniffed the half-finished cup of tea. Suddenly, she realized that there was a handkerchief under the table with the word " Yuan " embroidered on one corner.

She didn't pick it up. The book said that she couldn't touch anything on the scene.

She suddenly realized that her observation was too one-sided. There might be other clues here. Suddenly, Gu Xin's interest in solving the case was piqued and she looked around the house.

In addition to the footprints on the window and the handkerchief on the ground, she also found that there was something wrong with the wall of the house. The back that was covered by a painting was empty.

Since she couldn't touch the things at the crime scene, she could go to the room next door to take a look.

Hence, Gu Xin went to the room next door and confirmed that there was a painting hanging on the same wall as the one at the murder scene. There was another painting there, but it was crooked.