Are "Hard to find bugs" the responsibility of the developer or the tester?

May be it seems an open question (or non-constructive according to stackoverflow standards) .... but I am asking if there's something rigid according to Software process standards addressing this topic ?

If there are one or more "Hard to find bugs" that need complex scenarios, extensive testing, very big or special data set to show up ... Is this the responsibility of the developer or the QA ?