"....that the SBI couldn't find DNA even though CGM had sex recently wouldn't look too good either."
it might be as simple as SBI is only set up/certified to do RFLP and the private lab could do PCR; the latter being the process which grows or amplifies small amounts of DNA imto quantities adequate for full-scale testing.
That would mean the SBI did find DNA, just not enough to work with, but that doesn't match Cheshire's statements.
I can believe the SBI lab didn't have enough to work with on the fingernail.
I can't believe a vaginal swab wouldn't give them enough to work with.