If you believe the DNA belongs to the killer, then, you have a problem which must be addressed if you are going to use the fingernail DNA, also. If the fingernail DNA belongs to the killer, then, why is it so degraded as opposed to the longjohn DNA? I'm assuming, if the DNA does belong to JBR's killer, that it got there by JBR clamping firmly onto the killer's arm, face, etc. In other words, it must've come from the murderer's skin cells.
We know the fingernail DNA was harvested no more than a day and a half after JBR was killed, yet this DNA was very degraded. The longjohn DNA, also obtained from the murderer's skin cells, was harvested 12 years after JBR's murder and it is not degraded in the slightest. Can you see my point?
JBR scratches skin cells from the murderer; it is collected shortly after the murder and is terribly degraded. The murderer deposits skin cells onto JBR's clothing; this is collected years after the murder and is pristine.
I don't believe the fingernail DNA is a match but if it is, there is one explanation which fits. JBR handled something which left someones DNA on her fingers. She goes to the bathroom thereby transferring the DNA onto her longjohn waistband and crotch area. After doing so, she washed her hands thereby degrading and washing residue DNA underneath her fingernails. If this is true, I believe the DNA could have come from her bicycle handlebar grips.