Post-mortems are a terrible place for handling HR issues. I'd much rather they be kept focused on processes and technical details, and human problem be kept private.
Dogpiling in public is an absolutely awful thing to encourage, especially as it turns from removing a problematic individual to looking for whoever the scapegoat is this time.
One problem is that if you behave as if a person isn't the cause, you end up with all sorts of silly rules and processes, which are just in place to counter "problematic individual".
You end up using "process" as the scapegoat.
It's way too easy to pretend the system is the problem while sticking your head in the sand because you don't want to solve the actual human problem.
Sure, use the post mortem to brainstorm how to prevent/detect/excise the systematic problem ("How do we make sure no one else can make the same mistake again"), but eventually you just need to deal with the repeat offender.