Those outside US juristiction.
It is not a business in the standard sense, but any US state is also free from copyright prosecution thanks to the 11th amendment.
Then there are those that are useless targets. Try collecting from a disabled veteran where 100% of his income is from his VA check. You would never be able to collect.
If your target has deep enough pockets, and can't hide, they will often be on contigency. Most of those companies are not the sorts that get into wanton copyright infringment though.
That is a little off-base. It largely depends on which circuit your copyright suit is filed in whether "substantial similarity" will help you. And you still have to show copying. If we both take pictures of the Nisqually Glacier on Mt. Rainier, from the bridge downstream, at the same time and with the same disposable cameras, they will be substantially similar, but that does not mean that they are copies. No copying = no case.
That simply does not matter. Does he have transfer of those specific rights, to those specific works, spelled out in writing, with a chain of transfer of those rights going back to the original copyright holder?
The copyright code is quite clear that the transfer needs to be in writing. And the courts have made it clear that the writing has to be clear also. It doesn't have to be complex, but it needs to be clear.
And even if he thinks he bought distribution rights, removing the copyright notice, or modifying the work is not one of the rights that were purchased. Removing the copyright, in fact, is one of the things that will change it from simple infringement, which is a civil action, into a criminal action. You said that there was no attibution, but you didn't say whether or not there was a copyright notice on the original.
If he violated any of the criminal parts of the copyright code, get in touch with the US attorneys office. Barring that, you can file a local suit, which would force him to turn over the CD to you as part of discovery. And he would not like the results of not turning it over.