I've been thinking about this all day.
I cant think why someone would stop on or even near a bridge on the most main road through that area, (even though it was very very late) after travelling 20 minutes to get there, unless they particluarly wanted to dump the body off a bridge into water.
The Kholo Creek bridge is perfect IF you wanted the body to wash into the Brisbane River and disappear.
What if, GBC decided to go with the suicide idea, and drove Allisons body, carefully dressed in clothes he could identify to Kholo Creek to stage a suicide jump off a bridge, but not a main bridge where he might be seen doing it?
Notifies Dad of plan, and the 2 drive a car each 20 mins out there (as MM says, to an area he feels comfortable with) to stage a suicide.
Cars pull up on the bridge, precisely where the guard rail changes to the guard rail of a bridge, (see pics from Makara, especially the one with the photographer leaning over the guard rail- thankyou Makara.) He would assume that he was then over water, and in the pitch black, had no way of seeing that he wasn't. He drops the body, but oh f"^k, no splash!!!!!!!!!!! What the....????
Cant leave the car here now? Body will be found at daylight!!! Evidence of murder could be found. Plan was for the body to sink, drift into Brisbane River, be attacked by marine life and resurface a few days or weeks later, maybe only as a foot in a jogger, or part of a grey tracksuit???
(this was why he had a detailed description of what she was wearing)
Cant go down the bank. Too dark, too dangerous. Kids at home.....she must be close to the water, will probably wash into the river on the next tide anyhow....
Change of plan required immediately. Leave the body. Prob wont be found anyhow, but forget suicide theory and go with abducted while walking story.
When police visit the next day, they get a bit of each story, all muddled, cos lies are very hard to make up on the spot.