Which message key is used to check NCIC person files and simultaneously conduct a III QH transaction?

The message key used to check NCIC person files while simultaneously conducting a III QH transaction is QWI. This key is specifically designed for querying information about individuals in the NCIC database as well as accessing the Interstate Identification Index (III) system in a single transaction.

Using the QWI key allows law enforcement agencies to efficiently gather comprehensive data on a person, thereby enhancing their ability to make informed decisions quickly. This versatility makes it a vital tool for those needing to verify an individual's identity and any associated criminal history or other relevant records.

The other options, while related to querying within either NCIC or the III, do not serve the dual purpose that QWI does in conducting both checks at once. This highlights the unique functionality of the QWI key in the context of integrated data access.