What condition must be met before taking DNA samples from arrested persons?

DNA samples can be collected from arrested persons under specific legal guidelines. These samples are generally taken after an individual has been arrested for a qualifying crime, such as a felony. In many jurisdictions, this collection is permitted without needing a probable cause hearing beforehand. However, in jurisdictions with stricter policies, a probable cause hearing may indeed need to confirm that there was sufficient justification for the arrest before DNA can be collected.

In the context of the correct answer, it is crucial to understand that adequate legal procedures must be followed to ensure the protection of individual rights. The presence of a probable cause hearing can serve as a safeguard against unlawful invasions of privacy, ensuring that the authorities have a legitimate reason to gather such personal evidence before proceeding further with DNA collection.

The other options do not align as closely with legal standards for DNA collection. The presence of witnesses is not typically necessary for the collection process, and while supervisor approval might be part of internal department protocol, it is not a legal prerequisite. Similarly, the requirement for physical evidence is not applicable since DNA collection does not necessitate that other physical evidence be present at the time of an arrest.