There were four (4) red fibers on the tape, consistent with the jacket PR had on amongst many unidentified fibers not sourced to anything in the house. The supposed 'panty' fibers were discussed in an interview with JR, suggesting they came from his shirt, but despite his lawyer's advice, he replied
" 8 THE WITNESS: If the question is
9 how did fibers of your shirt get into your
10 daughter's underwear, I say that is not
11 possible. I don't believe it. That is
12 ridiculous."
So he was asked and answered the question. They showed no proof that they actually had such evidence, so he wasn't obliged to answer at all really was he?
It's been stated (and I have no reason to disbelieve this) that proof of this type of evidence is not usually provided to defence counsel until charges have been laid. I think the fact that charges were not laid speaks for itself (unless you're RDI of course!) This is probably RDI's main 'evidence' together with the RN 'expert analysis' (which is just a joke really) so naturally they need to emphasise and magnify it and continually refer to the fiber evidence, if it actually exists, as if it were significant.
Regarding the four red fibres (perhaps) from PR's jacket, I think that you could imagine both JR and FW comforting PR that morning and embracing and supporting her, so transfer is quite likely, especially following the discovery of the body when FW apparently went back down and picked up the tape.