You're either going to have logs pointing to an IP that the individual used to siphon your data, or nothing.
With an exposed elasticsearch database, you possibly had the data being siphoned by many parties, and are only aware now because of this particular incident.
If you have any operations regarding customers in Europe, you need to notify your relevant Data Protection Authority
https://edpb.europa.eu/about-edpb/board/members_en
You should also sign your engineers up for this course:
https://www.elastic.co/training/specializations/elastic-stac...