If they're low on resources why do the hub? Why not release the facial stills of the people they seem most important? Are we assuming they've had each vehicle forensically searched and discounted? I mean, out of the vehicles they must have spoken to owners to clarify why they were there etc surely they don't all have watertight alibis and if one isn't registered/fake plates/stolen etc then it makes it all the more likely to be the one involved.
The timeline itself really has to be 3.25-4am this can't leave them with too many options here. What about the neighbours of the car owners? Suspicious behaviours and anything unusual happening. If resource is really low why are the vehicles not the priority over some rather grainy footage?
I've said it before, I fail to see the huge mystery. Yes he could have arranged to disappear, arranged a lift or been taken unwillingly but if it comes down to four vehicles then what's the next feasible steps?