That exception was seen as a limited device to be used only in cases of an imminent safety threat, but the new rules give interrogators more latitude and flexibility to define what counts as an appropriate circumstance to waive Miranda rights.

A Federal Bureau of Investigation memorandum reviewed by The Wall Street Journal says the policy applies to “exceptional cases” where investigators “conclude that continued unwarned interrogation is necessary to collect valuable and timely intelligence not related to any immediate threat.” Such action would need prior approval from FBI supervisors and Justice Department lawyers, according to the memo, which was issued in December but not made public.