Quoted:
I would agree there. If there is nothing nefarious (whatever that may be) then why lie about interacting with Williams 4 days later? That part may not be in the article. What's there to gain? And why fail the poly (before walking out IIRC) when questioned on the consistency of your second version of events? I dont think we can say for certain what's happening here, but it doesnt quite smell right.
The pair of disappearances is suggestive, as is the deputy's claim that he called the store to ask about Williams when his phone records show that the call did not happen. It could also be bad memory and it could demonstrate that he didn't care enough about the contact to make up a convincing lie.
Regarding polygraph tests, I give them zero credibility. I wouldn't personally submit to one and I can see how someone might take offense, both personal and legal, to the process. It's an interesting story, but without some evidence that a crime was committed, it's just a story. Also, if the deputy was a serial killer of people he contacted while working as a police officer, you'd expect there to be a lot more disappearances and a lot more questionable actions by him.
If either of them turn up dead, he will have some serious explaining to do.