I find it so hard to connect EEG results to any particular mental states (worked several years way in the past, trying to do that for research on the mental states of normals vs. other DSM diagnoses). EEG's are really old fashioned - kind of like the work on brain measurements (without MRI's to measure brain function). Even MRI's are no longer the gold standard.
From what I can tell, neither MRI nor PET nor SPECT can differentiate DID from depression or other common mind/brain issues.
Horribly formatted abstract on this issue
here.
DID patients distinguished from normals
here. However, there was no attempt to distinguish the DID people from depressives, etc (so...well, not exactly a slam-dunk for the defense or Dr Lewis).
DID and PTSD - closely related in findings
here.
And of course, DID sufferers who plan murders and cover-ups are virtually unstudied. "Abnormal" PET and MRI and SPECT results do not yet differentiate among various disorders (IMO). Including depression, which is widespread.
Can we imagine a world in which someone like Chris Watts could give "proof" that he was depressed and get a NGRI???
I suppose we could be heading in that direction...I hope not.
IMO.