Reward: 1800 exp
After you have seen the site of the murder and the letter from the chest, in "A Mysterious Murder" quest you will receive a quest, in which the victim's wife is considered the suspect.
You can find Esmeralda at her shop. After you show the letter to the guard, he will be surprised that there is one more lover, apart from himself. Esmeralda will say that this does not prove her involvement.
To make sure about her guilt, climb up the stairs and find the key to her apartment. Climb downstairs and open the nearest door. First, search through the ground floor and you will find a book on how to plan a murder, on the desk. Return to the adjacent room and climb to the basement, through the trapdoor.
On the left of the stairs, there are rashers of ham hanging. Remove them to find a switch. Press it and the door to a secret room will open. Demand explanation from her. However, she will tell you that it is her husband's book and the knife to cut swine. She will also recommend that you take a better look at Evelyn.
You can ask the captain to arrest, or not to arrest Evelyn, for the duration of the investigation, which ends this thread and you will be able to focus again on "A Mysterious Murder" quest.