What do you think the odds are that the birefringent material was from the varnished paint-brush handle? Do you think the end of the paintbrush (that is missing) was used to assault JB? Or, do you think a bit of the varnish got on the perp's finger and that it was a digital assault?

Or, do you think the birefringent material was from something like a bit of talcum powder?

FWIW, I'd go with digital assault. I think the killer broke the paintbrush into three parts, throwing one piece back into the paint tote, using one for the construction of the garrote, and the third bit was stuffed in his pocket or misplaced amongst all the junk in the basement or rolled under something and not discovered.

Does anyone know what the 3 lengths of paintbrush were?