A jewelry exhibition is about to be held in a hotel. Miss Linda, who is in charge of jewelry design, took the jewelry to the VIP room on the third floor of the hotel. Mary, the head waiter, took Linda to the room, picked up a suitcase full of exhibition jewels and put it by the bed. When she left, she asked, "Do you need anything?"

"No, not now, but bring me a glass of milk tomorrow morning!" Linda said.

The next morning, when Mary delivered the milk, Linda was washing her face in the dressing room. Suddenly, Linda heard Mary exclaim, and then fell down with a splash. Linda put down the towel and rushed to the hall at once. She found Mary collapsed at the door and a stream of blood ran down from her forehead.

Linda subconsciously went to help Mary stop the bleeding. She hurried to find the pillow towel, only to find that the suitcase on the bedside table was missing. Linda was frightened and called the police immediately.

When the inspector arrived at the scene, Linda cried and told the inspector the cause and effect of the incident. Mary agreed, "Just now, when I was delivering milk to Miss Linda, a masked man came face to face. Before I could react, he was hit hard on the head. I saw the masked man escape with Linda's suitcase in a trance. "

When the inspector came to the bedside table, he saw a glass of milk lying quietly. He suddenly realized and said to Mary, "Miss Mary, shouldn't you tell us where your partner and Miss Linda's suitcase are?"

Obviously, the inspector already knew that Mary was responsible for the theft, so how did the inspector judge?