Riddle. Best answer = 10 points?

A crime had happened at a inn near the Nile river. A wise man came to the inn. Some one in the inn has stolen my wife's diamond the inn keeper said to the wise man. The wise man gave every person a stick. The stick will grow two inches if the owner has stolen the diamonds the wise man said to the people. The next day the wise man saw that a person had the shortest stick and he acused her of the crime. The woman amitted that she had done it. Why was the stick shorter? How did the wise man know?