49 CFR 5.93: Termination of investigation.

When the facts disclosed by an investigation indicate that further action is not warranted, the OST component or OA with enforcement authority will close the investigation without prejudice to further investigation and will notify the person being investigated of the decision. This notification requirement should only be applied where a subject of an investigation has previously been made aware of the investigation, or other pre-enforcement activity. Nothing in this section precludes civil enforcement action at a later time related to the findings of the investigation.