Known or suspected espionage should always be reported to which agency?

Reporting known or suspected espionage is primarily the responsibility of the FBI due to its role as the lead agency for investigating and preventing espionage and related threats within the United States. The FBI possesses the necessary investigative authority and expertise to handle these sensitive matters effectively, drawing on its resources to assess threats, gather intelligence, and conduct operations to mitigate any risks associated with espionage activities.

The FBI's mission includes protecting the United States from foreign intelligence operations and handling cases of sabotage, theft, and espionage, thus making it the appropriate agency to notify in these situations. While other agencies such as the CIA, NSA, and the Department of Homeland Security have roles in intelligence and security, they do not have the same focused responsibility for addressing and investigating espionage incidents as the FBI does.