Actually by not having documented proof from a third party, he's likely only screwed himself because the manager can just claim the damage is your fault for working on it without permission and evict you.

If there's any records of OP filing complaints- phone calls, letters emails, etc- then the lack of a third party witness won't matter. Having photographic evidence would also make it unnecessary. If there have been any inspections done to the building- which are supposed to be done routinely- that would be another way to make it unnecessary.