Under what condition may a person be legally searched?

A person may be legally searched if they are under arrest because this situation falls under the legal principle known as "search incident to arrest." When an individual is placed under arrest, law enforcement officers are allowed to conduct a search of the individual and the immediate area within their control to ensure the safety of the officers and to preserve evidence. This search can include both the person and any containers or items they may have on them at the time of arrest.

The reason why this option is the only correct answer is rooted in the legal standards established by the Fourth Amendment, which protects against unreasonable searches and seizures. For searches to be lawful, certain conditions must be met, one of which is the presence of an arrest, which provides a legal basis for searching an individual.

In other contexts such as when someone is a witness, volunteering information, or simply having a criminal record, those conditions do not grant law enforcement the automatic right to perform a search. Those scenarios might indicate certain circumstances or investigations but do not provide the same level of authority to conduct a search without further legal justification.