Need help back tracking

Hello,
I have a client running Exchange 2000 Standard with quite a few accounts on there, running pretty close to capacity.  It filled up some time ago, and I did 2 offline defrags within 2 weeks, bringing the size down to 9.5GB.  It stayed this way for a few months, and only grew by 100MB last a checked a couple weeks ago.  Last week the email services go down, and I find that the store is full again. I do the offline defrag and drop it back down to 11GB, and we put all kinds of policies in place.

My client now wants to know who was the offending mailbox that grew drastically in such a short time.  Is there any way to find out what the mailbox(s) sizes were at the time of the crash?  Thanks....