If he'd stored the images found on his computers of a girl who looked like Jo, being strangled, wearing similar clothes and in the same position/clothing state her body was left in BEFORE the murder, I would think that could be key evidence. I'm not talking about any old pics/violent game useage here, but some history that had a heck of a lot of overlap with the case.
Surely if that was date/time stamped prior to the murder you'd have to take it into account?