LeeAnne,
Do you think this is some new way to spam???
Duh, I forgot to suggest another source of evidence: the group's Activity Log.
Are there any incriminating entries in there from around the date/time of the spam posting, under "Mail", "Web", or "Email Commands"? Probably not "Membership" or "Moderator Activity", but you might look anyway.
Shal
Shal Farley