I'm not being flippant. It's not a question of what was required for you to register. Your requests to this web server are very likely logged, therefore subject to search by law enforcement. Depending on the details logged, your browser fingerprint will very likely uniquely identify your device and could be matched.

You should also understand that authorities do not seek that kind of evidence for violent crimes in the moment. Intelligence services capture massive amounts of traffic for future investigation. What you post today could be evidence for an offense you can't imagine ten years from now.