BBM - Somewhere (cannot find) I read that he (Jay) had the Runion's cell phone - did you read that anywhere? IF that is true...why would he have it? The very first time that he was interviewed - there must have been *something* to cause them to interview him. Obviously we don't know what that was - but there has to be some evidence. If I were on the jury and they could show me that he talked to them via cell phone, coupled with the location of their car and their bodies, I would be leaning guilty without any other evidence. They obviously didn't know him - they didn't have other friends in that little town - so what other possible explanation could there be for the Runions to have ANY contact with Jay???
IMO - unless he names another conspirator - all they need is one thing - a fingerprint, an item belonging to the Runions, etc. to seal the deal. Because they were only there (alive) for a short time...They were near his home...they were (or were suspected to be) carrying lots of cash.
I'm not jumping on you here - I just tend to go with the most plausible explanation and it usually (but not always) turns out to be the case. I remember when Jesse Matthew was on the run - and people had all sorts of conspiracies about how he may have been framed, just an innocent young guy going about his business and trying to flirt with a pretty girl, etc. etc.