Yes. My scenario does not make much sense. It would have be a case where she her mother was part of the problem she wanted to get away from. Another flaw in this scenario is that if she had a thought-out plan to start a new life, her stepfather could have revealed it to help police find who did it and to get suspicion off him. Another flaw is that the plan would have to be for Katelin eventually to admit to someone where she went. If the plan was for her to disappear, her stepfather would have known from the beginning that his lies in connection with her disappearance would look suspicious.
I struggle to think of an innocent explanation. I know he has no motive, that does not rule him out as a suspect. People commit crimes with no motive.
It makes me wonder how much circumstantial evidence is required to convict someone. If you say you took someone from point A to point B, witnesses show she was a point A but never at point B, and she disappears, and you have no explanation, it seems like there is probable cause to suspect you were involved in a crime. Maybe it takes a little more evidence to rise to the level of "beyond reasonable doubt".