I would have thought he would be open minded Cc? If foul play other than Sheila was involved it was his job to find it?
He should never have assumed it was a shut and closed case.
Surely he should be looking at the smallest marks and nicks? and the burns to Nevil's back should have aroused special attention?
But 4 police officers attended throughout the pm's and he was told as far as EP were concerned it was murder/suicide. He found nothing to contradict the murder/suicide theory.
Sheila has an unexplained graze to her abdomen but this is barely mentioned.
The marks will never go anywhere with the CCRC/CoA as they could have been adjudicated on at trial.