Re the truck driver theories, it's always possible this does involve someone who's worked in the transport industry, but it doesn't really make sense that the NSW parts of this crime were committed while someone was driving an interstate truck - long distance travel of the sort we're seeing really isn't at all unusual for people living in remote/regional Australia anyway (especially 20 somethings, or people who are into cars & recreational driving to begin with). When it takes 30 mins to drive from your house to the end of your driveway to get your mail, or it's an overnight trip to check your back fenceline, you can get a very different perspective on distance
Re Belanglo specifically, the trucks going to the quarry would be tippers or truck & dogs that do local work, they don't tend to do interstate runs unless they've just been bought/are being delivered to a work site.
http://www.salesandauctions.com.au/user_images/3216375.jpg
The trucks that
do work the interstate routes, like semi's, B-doubles & road trains, would be pretty unlikely to be taken into a Belanglo fire trail at all & certainly not without attracting a massive amount of attention - not even if they dropped their trailer first & drove in bobtail.
http://i.ytimg.com/vi/yFKufZ54DlM/hqdefault.jpg
If they did attempt it bobtail while they were on an Adelaide>Canberra run, they'd also have to find somewhere to safely leave their trailer while they drove into the forest & that would draw even more attention - it'd be noticed by every other truck/off work driver passing by because it would be such unusual behaviour (it's a good way to get your trailer stolen).
There are a LOT of trucks in this area of NSW, nearby Sutton Forest has a MASSIVE truck stop & many locals work in the interstate, intrastate & tipper industries (& there are lots of coal truck drivers from the mines around the Southern Highlands/Wollondilly/Wingecarribee/Illawarra too)
- someone in the industry would know this & I don't think they'd take the risk.
If they're an interstate driver they'd have to risk taking their very identifiable truck where it didn't belong & would instantly attract attention from the logging & quarry drivers. If they were a local logging or quarry driver they either had to take their truck into the forest at a time it didn't belong there to avoid attracting the attention of their workmates OR risk transferring Karlie from another vehicle to their truck so they could take the even worse risk of trying to get her up that fire trail during their work hours.
I mean, crazier stuff has happened, but IF there's a truck driver involved in this, IMO he had to have access to a car for Belanglo, I just can't see a driver risking it in a far more obvious & easily identifiable truck - & I'm not sure a semi could even access the fire trails without getting stuck, which is not something you'd want to risk under these circumstances.