Well, I was just thinking about the lint that accumulates in the dryer screen, how fine it is and how common and it's just fibers cast off from the laundry. It stands to reason that if he used the diaper on the gun to clean it, an easy assumption since he prolly used the diapers for that very purpose, that trace evidence from the diaper would remain on the gun.
Whether that trace evidence was left before the murder (say from an ordinary cleaning) or after when he wiped evidence off the gun, I say that at the very least it shows the gun is his, and in the latter case, it incriminates him.
Is Plourd making any headway?