So he enters by the window? The window is common property.
I’m thinking there might be an “OHS issue” here that required “immediate action to prevebt injury” – like spending a couple of hundred bucks on a joiner to board it up (once the squatter has gone out).
I’m serious – just do it and deal with the legal/Fair Trading/CTTT fall-out later.
I’m thinking chummy might get the hint and go elsewhere. What’s the worst that can happen – a rap on the knuckles from the CTTT? The rental agents can go whistle if they’re not prepared to take responsibility. And once this is done I’d have them hunted out of the building too.
It may not be the right thing to do and it probably isn’t the legal thing to do but I would do it.
It’s your window, after all.