Here's more on Justice Binnie from CK Stead:
Predisposed as he is, Justice Binnie is able to wave away David's brother's blood on his clothes; the broken glasses at the murder scene which were of use to David but not to Robin; David's fingerprints on the murder weapon and his handprint on the washing machine; David's admission that he heard his sister gurgling and that he alone knew where the trigger key to the rifle was hidden; the blood on David's gloves - and many other finer strands in that rope of circumstantial evidence. Instead of David Bain as the killer, Justice Binnie offers us (since there is no third alternative) a murder by the father, Robin, who must have worn gloves (why?) while killing his wife and children, then changed his clothes and put the blood-stained ones in the washing basket (again, why?) before killing himself, still with a silencer on the rifle (why?) and having first turned on the computer to write his confession rather than writing it by hand. Justice Binnie dispenses, it seems to me almost casually, with each of these elements, as with David's strange behaviour after the murders.
Signs of extreme stress would be expected; but what state of mind was David in that he made detailed plans for the victims' funeral; specified what lingerie his deceased sister Arawa would be dressed in; wanted the pop song Who wants to live forever? to be played for Laniet; told his aunt she was not to wear black at the funeral "because we see death as a celebration"; wanted to hold a posthumous party for Arawa on the Sunday after the murders; and spoke of "black hands" taking his family away? To me all this suggests a state of disconnection from the reality - a state of mind in which the crime itself might have been committed - as if the one who had taken responsibility for that (by every report) disastrously dysfunctional family was now ready to tidy it all away with a tasteful funeral.