> If the intern "had no experience with the AI lab", is it the right thing to do to fire them, instead of admitting that there is a security/access fault internally?

This wasn’t an accident, though. The intern had malicious intent and was intentionally trying to undermine other people’s work.

This isn’t a case where blameless post-mortems apply. When someone is deliberately sabotaging other people’s work, they must be evicted from the company.