Kitchen Leak Inspection Needed

Downstairs neighbor claims water damage to his kitchen from a leak above. I have no visible leaks, but suspect water may have escaped from an apartment renovation next door at the time the damage(fragments of falling plaster)was reported. The Coop Board claims without evidence that the pipe embedded in the concrete slab under the floor of my kitchen is private, not communal, making me liable for water damage. The building constructed in 1975 and the infrastructure has never been renovated. If there actually was a leak, it may have been caused by natural deterioration. I would like a report certifying the absence of existing or historic leaks from my apartment, plus determination of whether the underlying pipe is private or communal based on external measurements, building plans on file with management or available in the Adeje building department. Also, that the insurance company’s damage report is faulty and cannot prove my liability within a reasonable doubt.