This happened to me, but in my case, I'd cared for the dog for 2 years. I know the heartbreak of it, and I'm really sorry this happened to you and Ginger.
At that time I learned something very important; To always get it in writing if someone releases an animal to you for adoption. Then immediatly get the registration changed.
I would have called the police when this man came on your property. They could then have sorted out if the dog is registered, has vet bills or any proof that the dog is his, legally. They could have animal control look at the condition in which the dog lives to judge if they should get fines/warnings and such. The woman gave up ownership to you. And you'd cared for the dog for days. This dog could die of heat exaustion in hours, by the sound of it.
If the conditions don't change, call animal control. You really have no choice. Good luck to you. **hugs**