Reading Room Document
DOS Wiki: Duty to Warn
DOS internal wiki entry on the Duty to Warn (DTW). The wiki entry provides an overview of the policy under Intelligence Community Directive (ICD) 191, including to whom IC elements must provide a warning and which threats are covered by the duty. The entry notes that there are situations in which the duty to warn may be waived. Presumably, a description of these situations is provided as well, but those sections have been withheld.
The Intelligence Agencies' "Duty to Warn"
Documents released in our FOIA lawsuit for records on the U.S. government's "duty to warn" Jamal Khashoggi