You think this man the witness claims to have seen didn't have anything to do with it? If this man was actually with LS, on the night she went missing, then why would you think that he had nothing to do with it? Considering he was supposedly seen at one point slinging the girl (who was completely out of it) over the shoulder, what exactly do you think his role was? Or do you think the woman who reported it actually is mistaken about the identity of the female she saw that night?
Maybe it was just an acquaintance and he was already exonerated. I thought about this ... if that were the case why wouldn't LE confirm that witness account was corroborated? But perhaps they don't want to give that info away on the record. For instance, if they thought keeping that information from the person(s) they believe were involved would eventually yield more info, or if they thought it may give the POI bait for an excuse, or weaken their case, etc. ... Just thinking out lout, I suppose.