I don't know if anyone is aware of this, but I believe John Carnes' father was James Carnes, who was a police chief in MI for several years. I find that interesting. Especially since there were a lot of delays in the case.
I think they should be able to gather up all the circumstantial evidence and take it to a grand jury and let THEM decide whether or not John Carnes should/can be tried for Eric's disappearance. His statements, alone, make him look really guilty. And there's no way that he wasn't talking to Kendra about what was going on or what happened. No way. The car surfacing at a place where Kendra worked, and the neighbors seeing both John and Kendra there, is evidence enough. They knew where that car was the whole time and LIED. Why lie? Because you have something to hide. Plain and simple. And there's no way that Emily didn't ask her mother questions when she found Eric's cell phone in her mother's purse. Any normal human being, especially at that age, wouldn't be asking a million questions.