Is it illegal to "take" a dog that isnt yours ?

We are keeping this pit bull -storm. The first day (jay)-moms friend brings her over IN HEAT and ties her to the trEe with a male mixed breed. Well jay can't keep storm where he's living at so we are keeping her. And he said that if any of the puppies are mixed that he would kill them . Can I get someone else to keep her until she had the pups and until there atleast 6 weeks old ? It was his fault they got together he tied them to a tree together but storm is inside now. She is so sweet ! Can I just say she ran away ? And came back like 5 months later. ?????