Elderly couple mauled to death by dogs!

Authorities in Atlanta, Georgia, say that about a dozen dogs attacked a former college professor and his wife on a rural road, and mutililated their bodies.
Lothar Karl Scheder, and his wife Sherry were apparently just out for a walk.
My question is, how did the authorities know it was a dozen dogs, and where are they now? Is an alert out for people to beware of them? You can't help wondering how this could have happened. My guess is they were a feral pack that has been living off the land, and the Scheder's were probably their first human victims. Once bloodied, a dog will come back for more.
The only reason I mention this grisly event is that it's so unusual.