For me, it's the point that has not been refuted yet (and probably won't be)...and the point that I personally don't have a logical explanation for.
Agree - it's not THE thing, it's the thing that puts us over the edge, or - more telling - for me it was the thread that sewed together the fabric swatches of CE into a quilt. It pegged the cumulative hinky meter.
The VoIP phone data is just too confusing and when the FBI coulnd't find the "proof" and the Cisco expert couldn't say definitively HOW it was done, I think that turned rather sour. he COULD have, but we can't prove he did...
Everything else that was hinky, or odd, or made us dislike Brad as a husband could be explained on it's own with some less that sinister reason - not reporting her missing, the cleaning binge, the lack of allowance, the laundry extravaganza, the early AM Harris teeter trips, the shows, the mica fest, the clean garage, the clean trunk / dirty car dichotomy, lying to the police about the state of their marraige and scores of other things could be explained on their won by reasonable and plausible explanations. (could they ALL be explained, on the whole, as reasonable and plausible - probably not - but you'd simply want something MORE to convict someone.)
The map search of the area where Nancy's body was found - the day prior to her disappearing, for me, could not be explained. it was a coincidence that could not be rationalized even if we gave him the benefit of the doubt.
For example - no one really thinks he scrubbed the floors to make her happy - neither of them were doing ANYTHING to make the other one happy. But - it was *possible* that he cleaned. Not likely, but possible. I can do this same exercise to explain all sorts of behavior - not talking to her parents, not calling the police, not giving the allowance money, and so on.
What I can't extend the *possible* argument to - is the search. I can't even give it "remotely possible". so - that put the hinky meter into the red.
What I also can't extend credibility to is that there was collusion or fabrication of evidence by the CPD or in conjunction with the FBI. I don't believe CPD has the skills and I do believe FBI has the skills to figure that out.