Let me begin by saying I have no insider knowledge, simply sharing my opinion based on my analysis of the public information released.  Having said that, it's always been my practice to follow an Occam's Razor approach.   Keep it simple and try not to assume too much.  

Arthur John Vansice is the only guy after 20+ years that can't be cleared by law enforcement.  He's also the only guy who right away blurted out that he  “was the last person to see Jodi alive.”   Think about that.  He wasn't just 'the last person' to see her, but "to see her alive".  Why would he imply she was dead when this was only an alleged abduction at that juncture?  That is extremely disturbing on it's face.  Heck, I probably would have wanted to search him, his car, boat, home... Immediately.  

The relationship between John and Jodi has been described in different ways by John and Jodi's friends.   John calls it a Father-daughter type relationship where Jodi's friends tend to think John wanted a serious romantic relationship.  Consider John naming his boat after Jodi.   This 'father' was divorced with children.  Why would he choose to name it after Jodi?  He's already a real Dad.  I tend to agree John was courting Jodi with the gifts and attention. 

Let's face it, John was the guy that was always around Jodi.  He's a big guy compared to Jodi and would have little trouble controlling her physically.  He had the means and opportunity.  Police have said his time line from the previous night (B'day video watching) didn't add up.  His possible motive hinges on how he truly viewed the relationship.

I'm glad the police recently served a warrant on John because he's the top suspect in my opinion.  All these years with his precious Jodi missing and he's hardly lifted a finger.  Avoids interviews like the plaque.  Unless it's about him - "I passed a polygraph." I know if my love one was abducted I'd be doing all I could to keep the public involved, no matter if the police were looking at me. 

I realize there are tangential theories and sightings about stalkers and a white van,  but Jodi was very late that morning, and the risk of hanging around for someone who is aware of her schedule seems to me as a bit too much exposure for a snatch and run.  Jodi's normally gone by 3 am, and this likely happened between 4:15-4:30 am.

As has been repeatedly said, have to prove this beyond a reasonable doubt, so knowing, speculating and proving are very different things.  However, in my opinion, John is the guy to keep focusing resources on. Apparently, law enforcement shares this view.