Some dash camera systems have a feature called "buffered parking mode" or "motion-activated recording." When activated, these cameras can continue to draw power from the vehicle's battery and capture video when they sense movement or impact, even if the car is turned off. This feature is especially useful for capturing potential evidence or incidents while the vehicle is unoccupied.
However, it is important to note that not all police dash cameras have this capability, and the duration of the recording when the vehicle is off may be limited by the power available in the battery or a dedicated power supply. Dash cam use is also subject to privacy regulations and guidelines, and their operation may be controlled by the vehicle's power settings, department policies, or law enforcement procedures.
For accurate information on whether or not a specific cop car's dash camera continues to record when the car is off, it is best to consult with the local law enforcement agency or department that operates the vehicle.