A couple of questions , forgive me but I am a bit rusty on the case.
1) if the picture was taken before the swabs could it have been before the pathology report and by that time the hands could have been cleaned ?
2) as far as I know there is no proof that nevilles injuries (apart from shots) were inflicted before or after shooting?
3) purely speculation but Neville was fully aware of Sheila's violent outbursts so possibly his reaction to her hitting him or attacking him , possibly before the shooting, would surely be different to confronting Jeremy with a gun. With his background a fight with Jeremy would surely have been different than trying to calm a mentally ill woman?
4) I still think that looks like a full handprint in blood . But as the pathologist was not at the scene and he was convinced it was murder suicide then perhaps his report was not thorough enough rather than being deliberately misleading?