Allison was taciturn and reserved and not well at the hairdresser.
Allison the next morning had to attend an real estate event and had to look good (knowing most of the other participants probably would be informed about "ex"-mistress).
In a bad mood and with fresh hairdone Allison wouldn't consider to do a walk.
Arguement or not, around 11pm there is a terrible scream (Flegg). The murder takes place.
Allison dead or severe injured, GBC wraps her body into some sort of tarp. This tarp was perhaps stored in the open carport (4 diff. traces of plants).
GBC loads the wrapped body in the rearward car during which he pushes Allison's head (blood, hair in the car).
At Kholo Creek bridge or in the vicinity GBC unloads the body and fixes some straps. The straps GBC leads on his left neck side towards his right armpit (abrasions to neck, chest and near armpit). With his hands GBC holds under the belt to not cutting his skin through fabric (therefore bruising marks from hand knuckles).
GBC pulls this load (the wrapped body), perhaps abseils the body meter by meter.
Then the body is deposited under the bridge and has to be unwrapped, where the body rolls in the sleeping position.
Finally GBC needs help to dispose the tarp, the straps, his muddy clothing and shoes (cars, door clapping, voices at Kholo).
IMO IMO IMO
That's my version - today.