Lots of good responses here. That’d be a really scary find, OP, and I’m sorry you’re dealing with that. :(

As much as I also long for justice, I also totally understand the inclination towards just nuking and paving the whole thing and moving on. Some factors that occurred to me:

• Those posting it might be outside your nation’s jurisdiction.
• They might just be bots set loose by unknown actors.
• The above, plus they might be using “zombie” machines to bounce this material around unguarded servers wherever they can. It could be very difficult to ascertain who is behind this.

I agree with others that you should only move forward under the guidance of a good lawyer, because you don’t want to be the most convenient potential suspect they have access to.

If you could log their IPs or other identifying data and anonymously forward suspicions to authorities that would take action on them, that could potentially be a viable option. But again I’d ask a lawyer.