The burning question here is Exactly how did the CP get found in the first place? If it was secretly embedded inside some "normal" file, who would have found it? It certainly would not have been accessible to the defendant if that were the case.
However, if the CP was "extracted" into a viewable format, what magical means was used for this to happen? Did it do it by itself?
The normal examination of MAC times for last viewed, evidence of the actual P2P searches, etc should make this pretty easy to figure out.
However, it depends a lot on how many images, when they were extracted, were they deleted or kept.
Is there an expert on the other side who did a forensic examination for the defense?
Without the full story, it is always hard to say what actually happened.