The Sims 2: Castaway (DS) has a "Thief V" case in the **Mystery Island** chapter. You play as the Agent. Here's the solution path:
Goal: Prove the suspect (V) is innocent by finding evidence contradicting the accusation.
This is the only "Thief V" case in the DS Castaway story. Other versions (Wii/PS2/PSP) have different mysteries.