Which of the following is not a valid identifier used in criminal inquiries?

The selection of "Medical history" as the answer indicates an understanding of the types of identifiers used within criminal inquiries. Valid identifiers typically pertain directly to criminal justice processes and the tracking of individuals within databases.

Identifiers such as OLN (Operator's License Number), SSN (Social Security Number), and FBI number are all specifically designed for identification purposes in law enforcement and investigative contexts. They provide unique and systematic means to track individuals, ensuring accurate data handling and retrieval.

In contrast, "Medical history" does not serve as a unique identifier in the context of criminal inquiries. While medical history may be relevant to certain investigations or legal cases, it is not a standardized or universally recognized identifier for law enforcement purposes. Instead, it is sensitive personal information that is subject to privacy laws and is not utilized for the explicit tracking or identification of individuals within criminal justice databases. This distinction highlights why "Medical history" is not a valid identifier in this context.