I wonder if he had been fixated on her, and had been planning to capture her, for awhile. Then, when she and Charlie became a couple, he just sped up the process. We know he doesn't do well w/other men. What made me wonder was, that she'd been working for him, and then she and Charlie got together and he called them there to set them up. Charlie's mother had said:
http://www.greenvilleonline.com/sto...lues-after-body-found-kohlhepp-land/93315404/
Kind of like him kidnapping and raping the girl when he was 15. I believe he blamed his anger on his father, but that was a ruse. I think he'd been fixated on her too, but, at that age, had not yet figured out what to do after he kidnapped her. He had no way of keeping her.