No bodies found - just lots and lots of rat and mouse mess which Im guessing was the source of the smell. The space itself has 2 airbricks to the outside world, one either side to allow for ventilation but Roland is moving about in the wall cavity itself and coming in via the internal blockwork where the builders have just left a gap opposite the air bricks rather than installing a cavity sleeve. I've been watching it come and go on the camera, if I could get anywhere near it I would screw a bit of 1/2inch wire mesh over the gap that would stop that it getting access completely at least via that way.
It's been back twice since I cleared things out, it sets the motion detection on the camera off which sends me an alert but it doesn't stay - shame.
I'd been planning to move the kitchen back to the original room which would leave this space empty. I could drop the ceiling and fix things, making it rodent proof and then put some kingspan in there as it's now uninsulated. All subject to the usual Time, Money and Energy triangle though.