I have trained dogs for many years, and based on the handlers commands, the dogs can do a silent "tell", and then have another signal to "bark".
I bet the police wanted the dogs to make a ruckus, just to unnerve CW even more. And when they are allowed to "bark", they are so darn excited, wiggling their tails, they can hardly contain their excitement, because they know they have done a good job.
I won't go into detail on training a dog for search and rescue, but they are trained for scenting dead bodies, and live ones, and to react differently based on the scent.