How to find a large, rogue message in an Exchange 2003 Message Store

We have about 500 mailboxes on a message store and the usage just went up by 10 GB in 1 day.  Our CIO wants to know who the offending user(s) is that used up the space be I can't find an easy way without going to every mailbox to determine who has the large message(s) that caused the space to disappear.  We don't have mailbox limits (we're a law firm) so I have many users with 10, 20 even 50 GB mailboxes with thousands of folders so manually looking is out of the question.  Anyone have any good tricks, tools, etc to help?
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Use ExMerge to find all messages for the last 2-3 days. Then from the Output do a search on mails based upon size this will give the desired output.
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