I have forgotten why it matters whether he buried the usb stick with him butt-plugging a trailer hitch, or someone else did?
Is it because of the possibility that any pics it may contain of Madeleine may not have an identifiable male in the pic too?
It matters because it may point to other people being involved with MM's disappearance or the abuse of other children perhaps by more than one person. It matters because a good lawyer is going to try to refute any evidence police have if ever they get the chance to fight charges.
So police might say: "hey we have evidence that CB is in photos / video with X doing X
Lawyer might say: 'oh yeah? prove it'.
So at that point, police might say, "well, here are the images / video - oh and we found them on his property buried with his dog."
So then a lawyer might say, "ah yes, now prove that is my client in the offensive criminal material.
Cop: "looks like him, and was found on his property" (which might be why they want to know details on the inside of his prior residences - corroborate location where this material was created).
Lawyer: "so it looks like him, but can you prove he created it?"
Cop: (lets hope they can prove he created it / participated in the creation)
Lawyer: And how did you find this material?
Cop: "It was on his property beneath remains of a dog...."
Lawyer: "So someone buried it with the dog, but can you prove it was my client"....??
See roughly how this goes? Cops need to show not just that they have the material, but where it was created, when it was created, why it was created (personal use or for sale or ring use), who else may have been involved if anyone....
The point being, if someone else buried it with the dog remains, it might speak to someone out to get CB, by placing evidence where police found it... its possible they have someone as a witness who gave up the info on where to find it and what was on the devices.....
Its clear in my head, I promise, just perhaps I'm not articulating my thoughts well.