I don't know that RD is actually a CSO. The people he molested were mentally disabled young men. Then he was creepy with his customers who were teenage girls so that they stopped coming into the shop. For him to take a young child as victim would to some extent be a new kind of crime.
Yes, that stood out to me as well - that William would represent a completely different kind of victim for him. I don't know well enough to make any sort of judgement. I'm aware that sex offenders, particularly child sex offenders, have patterns and target particular ages & genders, but I don't know what the prevalence of exceptions or variations to it are.
But otherwise he looks good on paper.
CSO (he has been labelled that so I'll stick with it for simplicity purposes) who at the time was not known to be one, so had less reason to worry about being suspected of anything if he was caught, say, talking to William. Was charged almost immediately after William's disappearance with a host of offences, preying on vulnerable intellectually disabled people, and it was something he was actively engaged in doing around that time.
He volunteered for the SES from memory, and people are not going to be suspicious of an SES person being around anywhere. Also gives him reasons to be in the thick bush across from FGM house and would increase the likelihood of William trusting him. He used his position in the SES to groom and harm the young men and had gotten away with it for awhile, so he was familiar with deliberately using his position to prey on people and possibly had quite a bit of confidence around his ability to evade detection.
He was not just a nasty creep, he was weird. Weird behaviour could fit with a random snatching. But on the other hand it seems his other CSOs followed a particular pattern of ongoing manipulation.
He was known to sleep at the Showgrounds just near FGM house when he wasn't working at the Caltex.
He participated in the search afterward, yet refused a police interview. I'm loathe to judge people for asserting their rights in situations, but I do struggle with him wanting to help such that he searched yet not wanting to help by providing information. That doesn't seem consistent. On the other hand, he clearly had a whole lot of other stuff he was being/about to be busted for, so he had other completely unrelated reasons for not wanting to talk to police.
He doesn't have a clear alibi and, in fact, provided dodgy looking documentation to claim an alibi. Of course, if his work records were accurate, even if the version of them he provided wasn't accurate, that's likely the end of that matter, so he could be a total red herring.