Final answer:
Carlos is likely a serial killer, as he murders wealthy middle-aged women whom he convinces to leave him their property, demonstrating a premeditated pattern.
Step-by-step explanation:
Based on the information provided, Carlos is most likely a serial killer. A serial killer is someone who murders three or more people, usually in service of abnormal psychological gratification, with the murders taking place over more than a month and including a significant period of time between them. Carlos fits this definition as he targets a specific type of victim: wealthy middle-aged women, gains their trust, convinces them to make him their sole heir, and then kills them, which indicates a pattern of premeditated and serial criminal behavior.