In the context of a good practice in context on how to perform a no blame post morten review, with a view to process improvement.

If a major issue is found in an application after it has been released (a test escape) who/what should ultimately be considered responsible?

• The developer for introducing the issue?
• The tester for not finding the issue?
• Both the developer and the tester?
• No-one (it's the system that failed, not the people)
• Everyone

Thoughts ?

Note: No actual persons were harmed in the writing of this question.