Why did the cop tell him to apply both the brakes and the emergency brake? Sounds like the cop must not know much about cars. Applying the brakes engages the front and rear brakes, applying the emergency brakes engages the rear brakes only, which is already engaged by applying the brakes.
Some cars use completely separate pads for the emergency brakes. My old LeBaron had disc brakes in the rear but inside they had small drum brakes as the emergency brakes. I know it probably doesn’t matter, but unless you’re just locking up of the wheels, it would give more grab.