I find personally just my opinion and agree with Mark Williams Thomas that it would be ludicrous of a gulity JB to have put the silencer back in the cupboard. Its my opinion he would have disposed of it or at least throughly cleaned it.
He would not have to be backspatter expert. He would have been aware that the silencer had come into contact with shelias skin.
I struggle with the factor of Nicholas's blood wasn't found in the silencer.