My guess is GBC's done the deed at their place then called his father who'ds driven up to Kenmore, parked in the Village car park (directly behind the bus shelter) and has gone to wait at the bus stop so GBC can pull in and pick him up on his way through to Mt Crosby to dispose of the body.
GBC may have pulled into the village on the way back to get rid of evidence in industrial bins which are on the bus-stop side of the village (afaik). All this coming and going from the village would have been right in the sights of the traffic camera. This explains the industrial bin lead and how they knew to look there.
I totally get that noone would have been thinking clearly at the time if this is true - but I can't understand why on earth Bwana would wait in that bus shelter in the most public place in Kenmore? They live in Durness St, which is kind of on the way to the roundabout from the BC residence - why on earth wouldn't GBC have just dropped in there and collected him? Why sit at the bus shelter for all to see? Not sure if I'm flying with this one.