I see what you mean, but Sheila could have made him - so no third party.
Isn't that what DCI Jones thought may have happened?
Yes, SC
could have forced Nevill to make the phone call.
So then we have to establish the case against SC.
I had previously given importance to the fact that she had smoked cannabis within a week of the murders. However, she had done this many times before without entering murderous rages, and there is no evidence that she was in a downward spiral in the days leading up to the crimes. She may not have been 'normal' in societal terms, but she was her version of 'normal'.
The more I look, the more evidence piles up in the 'SC innocent' table. The evidence against her remains the (uncorroborated) phone call and the fact she suffered from PS. It's not enough.
If JB's team refuses to explore the 3rd party angle, it doesn't leave much room to manoeuvre around the case.