If this is a lie, then why not investigate, study the evidence that Russia is ready to provide, and bring Russia to clean water? Why did the US, UK and France vote against this at the recent UN Security Council?
To prove what exactly? That Ruskis are lying? I think we are long past that point now.
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.
Anyone can make an unsubstantiated claim. Claiming something doesn't make it true, any more than making an assertion or stating your opinion equates to proving something. I could claim that I'm the King of Mars, but that would be a silly thing to do. And if someone believes me without any evidence, then they're just as silly as me.
If you want people to believe your claims, show them evidence. Fuck that "Nazi" part by the way.
Russia claims that it has documentary evidence. But the representatives of the United States, France and Great Britain in the UN Security Council refused to consider them and blocked the investigation. This is a very handy strategy for dealing with inconvenient facts - just declare them to be Putin's propaganda and pretend that the facts have ceased to exist after that.