the site has a copy of the content of his site on it
That's easy to take down, DMCA all the way as I've nuked sites for much less.
Proof is in the Internet Archive, go check the Wayback machine to prove the theft and if you're lucky and it hasn't been too long, old search engine cache pages if they still exist.
If they're in a land with comparable copyright laws, I'd hire a lawyer and simply file a copyright suit against him. If you actually copyrighted your content, the major mistake everyone makes by failing to file a copyright, then you can get statutory damages in the US per the DCMA and clean him out, crush him, reduce him to living in a cardboard box.
However, amusing thoughts aside, I'd proceed as follows which has worked every time:
- File a DMCA to the new domain holder with proof and also to Google, Bing, etc.
- File a DMCA with his hosting company which, if in the US, is required to remove the site to comply with safe harbor provisions.
- Send a legal C&D (cease and desist) letter giving a timeline to comply or face further actions. As part of the C&D demand taking down the site and return of the domain with 15 days to comply.
- Meanwhile, since the site went south and the owner lost everything, you should consider a new domain name and starting over as you're losing money waiting on the return of the old domain, which could be NEVER. Just make sure the DMCA's go out to eliminate duplicate content, otherwise you need to start rewriting everything to boot.
Good luck!