Email spam is hard to track, but if the spam is being sent by a real person, to somewhere like forums,  then it would be reatively easy to trace as long as the site keeps accurate logs of the IP addresses used by users when they sign up.  So, if the spammer was working from home, then they should have the spammers IP which can be traced back to their provider, and hopefully the spammers ISP also keeps logs of IP assignments. 

I worked as the only technical person for an ISP in MI for many years, and I had to deal with this stuff on a daily basis.  Most ISPs keep accurate records and are very consciencious about zapping users who are spamming.  It is in their best interest to do so.  If they don't, then their domain(s) and/or IP range(s) could end up on peoples blacklists and then none of their emails would get through.