I feel the same.
I know there's a slight possibility that it is some cryptic clue that could unlock the whole puzzle.
Yet I tend to think it's really just some random nothing, and though I appreciate my fellow posters who delve into it, IMO I'd prefer LE focus on more substantial clues.
It is of course discouraging that after five years, we have a video and perhaps DNA and a line-up of very creepy suspects, but the case remains unsolved. I think that's why at this point we just scour every tiny thing for a clue. But as
@StarryStarryNight noted, the information about "f" is so vague that it could or could not be relevant, but I lean on the side of irrelevant.
Jmho