My current thoughts.
Person of dubious character (AJ) parked outside a house on a day in tandem with a grey vehicle, owner of which unknown, but safe to say is an equally dubious person, if not more so.
Were they simply meeting there as it was a nice quiet street in which to do nefarious type "business", or was it pre-arranged?
If pre-arranged, by who, and how did that person know that kids would be there that day? It's a highly unlikely scenario, IMO.
If they were there purely because it was a quiet street, did one or both of them take the opportunity of grabbing a little boy who may have thought the car was his dad returned home, or were speaking to him about spiderman?
If it was opportunistic, why did they snatch a young boy? I can't see anything in AJ's former criminal history that would suggest he had leanings toward little boys, but he may have thought quick, and known someone who did. Therefore taking William purely with the intent of passing him onto someone else in the hopes of a $$ reward.
Did he have leanings toward young boys and just kept it hidden? Possible, though I thik the money scenario feels better. Howeverm the other dubious character is an unknown, and it may have been that person who had the urge to take William. In which case AJ may roll on him.
Think about it. They were both parked with windows down. One had possibly moved to the others car. They were discussing whatever deals they were making, and they could both clearly see little William, his sister and mum all outside playing. Cue mum and sister going inside, a minute or two ticks on, are you thinking what I'm thinking P1? I think I am P2, they lure William over, chuck him in the car and off they go. Or maybe one did it and the other one got the hell out PDQ.
I sincerely hope that this is the case, as that would mean since they have one of them, it will only be a matter of time before they get the other one, and some more information will spring to light. Which is why it has been stressed "somebody knows something." Like the current whereabouts of William, or at least the conclusive tale of what really happened, who it was in both the cars that day, who took him, why etc.
If is was more orchestrated than that, then it could be a deeper web where the truth is harder to get to.
Maybe police are hoping for a jailhouse confession from him, which happened in the Louise Bell case with the perpetrator, Pfennig.
I do think the cops are at least 2 steps ahead of us, if not more, and when they have released information, they already know what's what. They have said from the beginning it was purely opportunistic. They knew about the cars from the outset.
I think if two men were waiting around with the sole purpose to snatch a child they knew was at the property, then there would only be one car at most, and the windows would have been wound up. The car/s would also have spent far less time in the street.
