Also, make sure you can determine IF this is an actual person, and not a spammer computer.
Once you do a WHOIS Report, if the WHOIS shows that the IP Address belongs to someone in the USA, call THEIR Internet Service Provider, and tell them about it. Make sure you have as many details as possible, including any name that you know of, their IP, and their hostname if you have it. Many people have Dynamic IP Addresses and can not be easily tracked down, even by their own ISP.
If you determine that a computer is giving you this kind of SPAM, look into Post Moderation (where users under a certain amount of posts, say under 5 posts, must have their posts verified by a human moderator before being posted)
Until the issue can be cleared, you might even look at disabling the ability to upload attachments (if they are uploading it to your server).
Also check out Akismet for computer spammers:
http://custom.simplemachines.org/mods/index.php?mod=544If you think its an acutal person, and the FBI isn't doing anything, call (or visit) your local police station (do NOT call 911, call their buisness line).