Search Cases Using Business Data variable
If you want to do that, you have to register in your BDM the case ID.
By conception, the BDM and the process are independent. A process references a BDM and can manipulate it at a moment, but keep in mind MULTIPLE cases, MULTIPLE processes can register a BDM value.
So, by conception, if one case is important for your BDM, you have to create an attribute "myImportantCaseId" in your BDM, and save it when the case creates / modify it.
Second solution, the link between the BDM and the case is stored somewhere in the Bonita Engine database (until the case is not deleted), so you may find a SQL to find this relation? Of course, when the case will be deleted, this information will be deleted at the same time.
Hope this help,