That happened to me, long ago. I had some knowledge of who the perpetrator was and had success tracing his IP addresses and domain hosts, making copies of access log files (including his attempts to hack my server), and e-mailing the perp and (most importantly) his service providers cease-and-desist letters. I even discovered where the guy lived. Once his ISP and domain host threatened to close him down, he had to comply. Sadly, to make up for his losses, he immediately copied some other person's web content, thinking that wouldn't get noticed. And tried some other stuff against me that fortunately didn't work. (A bona fide sociopath.) Hopefully, that guy and his crew moved on to a better way of life.