Honestly, I don't think your organization is getting crappy PR. That's taking it a bit far IMO.
For all you know, the suspect stole the clothing!
Regardless, this will blow over (see
the Streisand effect for my rationale). I wouldn't give it any more attention.
ETA: if you really want to do something, this is a good opportunity to remind actives/alumnae about correct disposal of items that have identifiable information (e.g. cut the letters off the shirt before you throw it in the bag for donation. It can be sold as "rags").