Why didn't Ransom just kill Fran and stay on Marta's side?
She already agreed to give him his original cut if he kept quiet and helped her. When Fran contacted him the next day, all he needed to do was kill her, like he did anyways, and then stay on Marta's side. I guess there's a chance Marta could have refused to pay him, but I think she would have.
I just don't see the upside in going back to getting Marta caught and ruining her inheritance. He already won. Plus his family would be getting nothing, he'd be the only one with any money and he could rub it in their faces.