Having a registered trademark makes things easier... however, I do not believe that is required.
The Copyright Act of 1976 is /reasonably/ readable: http://www.law.cornell.edu/uscode/html/uscode17/usc_sup_01_17_10_5.html
I want you to pay special attention to § 505 which allows a copyright holder to recover costs (i.e. filing fees) and reasonable attorney fees (i.e. not-for-profit law firms live off these kinds of cases).
§504 of the act provides statutory damages as follows:
(2) In a case where the copyright owner sustains the burden of proving, and the court finds, that infringement was committed willfully, the court in its discretion may increase the award of statutory damages to a sum of not more than $150,000. In a case where the infringer sustains the burden of proving, and the court finds, that such infringer was not aware and had no reason to believe that his or her acts constituted an infringement of copyright, the court in its discretion may reduce the award of statutory damages to a sum of not less than $200.
Also, you should be aware that since you have a written admission from the malefactor, proving up your case has been made significantly easier (and the willful and continuous nature of his act makes the statutory damages much worse).
I am not an IP attorney -- If you want to take a serious step toward defending your copyright you need to seek legal counsel by an attorney who focuses on copyright infringement and copyright law.
I've seen some offers further up the chain to put you in contact with an IP attorney -- that would be a good idea.