For example, that in one of the psychiatric hospitals near Kharkov, biological experiments were carried out on incompetent patients without their consent. Or that in these biolaboratories plans were developed for biological contamination of Ukraine through the water system of rivers. Or do you think Russians always lie and this is an integral feature of their nationality? Well, in that case, you are an ordinary Nazi.
That's prety much same stuff like combat mosquitos and pigeons with chemical weapons, Ukraine preparing to use ''dirthy bomb'' or Tesla factory in Ukraine where missiles for HIMARS is produced. Russia already lied so much already that I'm not sure how someone still can seriously look in their claims. People who make such claims, indded, it's their integral featue to lie. And the rest of nation is just victims of brainwashing machine.
Anyway, IMO these organisations, including UN is just such pointless thing and most what they can do - say that they're deeply concerned.