I've been part of such retrospectives, and no blame is given, and no apologies are given. There is no hesitation to lead the investigation into "your own code". "Your code" might end up being what needs to change, but it was not alone in causing the fault in the entire system.
Another though experiment (stripped of all moral judgement):
Alice writes some code which runs as part of a larger system for 10 years. No problems are identified in the system.
Bob writes some code. After Bob's code is integrated with the rest of the system, problems are identified in the system.
Changes are made to Alice's code which resolve the problems.
Who is at fault? You probably find it hard to identify who is at fault without knowing more details. You need details so you can form your own personal moral judgments. Perhaps a better question is: Can we ever objectively identify who is at fault? And does it matter?