Ideally you should have a clear audit log of all developer actions that access production resources, and clear records of custody over any shared production credentials (e.g. you should be able to show the database password used by service A is not available outside of it, and that no malicious code was deployed to service A). A lot of places don't do this, of course, but often you can come up with a pretty good circumstantial case that it was unlikely that exfiltration occurred over the time range in question.