It was only a practice session for what hopefully would never be the real thing. The scenario was a response to an armed threat. Two policemen played the role of criminals who were planning an attack.
Police swarmed in and treated the situation as if a bomb might be involved. The SWAT Team approached the car, one of the assailants jumped out with a gun. He pointed it at the police ready to fire, and the police took him down.
They then checked the car for other weapons and explosive devices. Once it was all clear, they removed the "acting" assailants.