Finding Leaks in 2 ft of Concrete

I live in an apartment building where the bathroom walls and floor are made of brick/ cement construction. All of the pipes are buried in a thick layer of concrete.

Our bathrooms were completely renovated, but not tested before closed up. The neighbor downstairs had water leaking behind the closet but no one can tell from where.

Is there any way to be able to find the leak without breaking everything? I have been to websites where they suggest doing tests by running the water and looking below for leaks. This seems difficult because the floor is several feet thick. There is not one specific place showing drips, but rather mold and warping all of over the wooden closet installed in front of the concrete wall. We can see an area of the ceiling and wall that is damp.

We have spoken to several plumbers and their suggestions are to break everything and redo the entire bathroom. Please help!