Under what condition can an affidavit be based on a named informant's information?

When an affidavit is based on a named informant's information, it is most valid when the informant has firsthand knowledge. This means the informant witnessed or directly experienced the events or information that they are providing. The reliability of the informant is significantly enhanced when they can provide direct observation, as this gives law enforcement a tangible basis for the claims made.

Additionally, firsthand knowledge generally adds credibility to the informant's statements, making it easier for law enforcement to establish probable cause when seeking warrants or taking further legal action. In contrast, if the informant is anonymous, as mentioned in another option, or is simply sharing information without firsthand experience, the affidavit may not hold the same weight in a legal context. Therefore, having firsthand knowledge is critical for ensuring the integrity and reliability of the information being presented in an affidavit.