As Mr. Utterson’s character develops, he becomes more worried.
You can see in the first excerpt that he is really enthusiastic about his work and that he wants to find out who the criminal is. However, over the course of the following two excerpts, you can see that he is growing more and more worried about not finding the criminal yet. Phrases such as "under a weight of consideration," and "sobre spirits" tell you a lot about him worrying.