In my webslomnia overnight, I started thinking about this crime from a different angle, trying to get inside the mind of a criminal mastermind. Clearly, I'm not and neither is GBC - not such a bad thing.
IMO, GBC fairly quickly determined only two alternative versions would clear him: suicide and misadventure. There was more circumstantial evidence favouring the former, but only the latter would see him paid her life insurance, hence IMO the insistence to police early that there were no mental health/medication/relationship issues (this assumed prominence later, when his own liberty became more important IMO).
So, I think there were only, in each case, just a few more things GBC needed to do in order to make either credible, to my mind at least. As you would appreciate by now, I mean no disrespect to Allison in writing this, just thinking from a defendant's perspective.
Misadventure
1. Admit the scratches were inflicted during an argument about the resumed affair/not attempt to conceal them;
2. Concoct that Allison fled the house, on foot, in an agitated state;
3. Not get blood in her car;
4. Not get plant matter in her hair;
5. Not recharge your phone, or say you did because you were awake, worried sick;
6. 'Cleanse' A's handset (as nothing incriminating's been found via the telco) and leave it in plain sight, at home or on her person;
7. Deposit the body closer to home, but inflict further injury in doing so to both mask existing and suggest a violent (other) attacker;
8. Remove A's jewellery;
9. Approach the required phone calls in the correct order and act at least 30% more normal.
Suicide
1. As above;
2. As above, but by car;
3. As above;
4. As above;
5. As above;
6. As above, but leave it at home;
7. Deposit the body at the bridge, but over rather than under it, in order to inflict injury consistent with a fall from that height;
8. Leave her car at the bridge;
9. As above.
He might just have gotten away with it. What do you think?