Establishing personal identity in cases of DID

In some recent criminal cases in the United States a defense has been mounted based on an affliction known as Dissociative Identity Disorder (DID) (formerly Multiple Personality Disorder). The crux of the defense rests on the proposition that a dominant personality was incapable of appreciating the nature and quality of wrongfulness of conduct caused by an alter personality. This defense has been successful in some cases, but not others, and so philosophers, lawyers, and psychiatrists are now in debate in an attempt to clarify the issues. One of the salient issues involves the question of personal identity between the individual who allegedly committed the offense and the individual who stands accused. Stephen Behnke and Walter Sinnott-Armstrong have recently put forward a test for establishing personal identity in these cases. In this discussion, I present reasons for rejecting their proposal.