Actually - I didn't think of that. Kid could've bought stuff for Sims. Mom sees other charges. Kid says it was stolen and/or fesses up and police get stuff from Sims' apartment.
Stretch - but possible I suppose. It would be an easy explanation of how they got from missing CC to Sims.
Or, the kid could have also just given Sims and/or GF the credit card to use.
These become a huge problem if mom or son have any ties to ISU...