Former CIA officer breaks down 'duty to warn' requirement that saw the US give rival Russia a heads up before the attack in Moscow

• Ex-CIA officer Laura Thomas explained the 'duty to warn' protocol, that sounds the alarm on threats.
• The protocol is a tool to save lives and also communicates the CIA's knowledge to adversaries.
• Before the March 22 Crocus City Hall attack, Russia dismissed the US warnings.

The US intelligence community notified Russia of a potential threat head of March 22 Crocus City Hall attack under the "duty to warn" protocol, a requirement that a former CIA case officer broke down in a series of posts this week.