Unless one of them had a good reason for being there that day, which he could have used to explain his presence, if needed. Then nothing would have to align. Also, they are big blocks in that estate, so neighbours' vision wouldn't be as clear as in the usual suburban row of houses all with their driveways at the front near the road, especially when you add in the 'trees' factor. They provide good cover and also impede vision.
I also remember right at the start Jubelin saying something like everyone was a suspect (not his exact words) until they could rule people out. Don't have the link handy so I'll have to say IMO. I also don't think he'd have repeatedly used the phrase 'evil and innocence collided' without something to base that on.
Sometimes traps for these pedos takes months to execute, and of course the historical ones take much longer again, so IMO it could be difficult to move quickly. There have been a lot of arrests lately, all over Australia, and I do believe that at least some of them have to be a consequence of investigations into this awful case.
BBM.
Not to mention p&g that any perpetrator had the option of snatching William, physically restraining him and keeping him quiet, whilst taking off up the bush track back to the cemetery where they had conveniently parked their car. This, in my mind, would have been the most likely MO (including 'getaway' route).
Let's see, the only time William's FM said she noticed the white station wagon and the 'green-grey' sedan parked across the street from FGM's house was early in the morning when she opened the curtains to the largest verandah (I don't know about other children but my grandchildren get going at sparrow f@rt approximately 365 days of the year so I guess at the very latest, that would've been 7:30am?)
Then, all is well until approximately 9:30am (not long after FD leaves) when she saw the same/different(?) green-grey sedan drive past the house while the kids were riding their bikes in the driveway.
Again, nothing was out of the ordinary until approximately 10:25-10:30am when William ran around the corner of the house toward the sloping backyard and disappeared. No cars were seen or heard driving away, no scream was heard from William, no one was seen running from the house whilst restraining/carrying him.
My thoughts:
Someone saw, heard or knew William was at 48 Benaroon Drive that Friday morning.
They took a long shot that they would remain unseen; and/or knew that many of the houses were vacant (most particularly No 51).
They also either knew the normal daily routine of the residents and regular passers-by or had watched them leave that morning.
They either knew Benaroon Drive and its surrounds like the back of their hand or they scoped out the area within a few hours, including a getaway route.
They either watched and waited for the most opportune time to snatch William or he was in the wrong place at the wrong time.
Person most likely to have abducted William (IMO and in no particular order)?
The driver of the 'green-grey' sedan (either alone or in conjunction with the driver of the white station wagon),
and/or,
Someone in FGM's social circle/church congregation/street/wider community who knew where she lived and that William and his FF were coming to visit on Friday,
and/or,
a local bush/dog walker.
Whoever it was, they had/have a 'close connection' to Benaroon Drive and, even if they weren't seen there, I don't think they're going to get away with their crime(s) forever. IMO It's just a matter of time until a connection is found. If William has been abused or murdered, the perpetrator(s) will pay with life in prison.
