I think your second scenario is closer to their reason. I don't think the killer was on that kind of radar but still is someone known by many. I'd have to assume that no better image was found on that recording or this would have been solved before the funerals.Devils advocate: If he was known to them, why did they start recording him as he approached? Or are you thinking not in the good "their uncle did it" familiarity but instead "Holy crap, that's creepy Old Man Murray from up the street who is always ogling us from his front porch when we ride our bikes." ?
I'd like to know, what, if anything, was said by the victims in that recording.