It was the first time that one of the two Integrated Resorts was participating in such a large-scale exercise.
It started with a suspicious package in an auditorium that no one noticed. Soon smoke filled the room and guests were evacuated.
Not long after, a second parcel exploded outside the theater and three gunmen stormed into the Universal Studios theme park, opening fire, and leaving scores injured and dead.
Security agencies were alerted and deployed to the scene.
The simulated exercise involved some 400 Resorts World staff and officers from the various Home Team agencies, including the Special Operations command team which later subdued the gunmen.