When an ATC controller observes an aircraft squawking SSR Code 7500 (Unlawful Interference) or receives discrete notification of a hijacking, what operational protocol MUST the controller follow under ICAO Doc 4444?

1. Immediately broadcast to all aircraft on frequency that a hijacking is occurring on board the target aircraft
2. Avoid giving instructions that might escalate the situation, confirm the code discreetly without alerting perpetrators, alert authorities, and provide continuous ATS support
3. Order the aircraft to execute an immediate 180-degree turn back to departure point
4. Cancel all radar service and delete the target from the radar display