I bet the step dad didn't do it alone. He couldn't have gotten back out of that sink hole alone. It might have eaten him up! I don't know how these sink holes are in MO, I haven't been here long enough I guess, but down in OK where I was from... if you got in them, they would sink in on you at times and get you! This one seemed more like a cave / sink hole though... but he was big and it seemed like it was DEEP. I don't think he could have gotten back out!!!
If they couldn't get back out, then I've got a better solution than prison. Let's just throw them down the sinkhole and fill it in.