:::::Unreliable has a particular meaning in relation to a legal case - which I think expresses the situation well. "worthless" is a rather emotive choice of word, and the sort of thing we'd discourage against in neutral writing. Particularly because the context of the sentence relates the word specifically to how the experts testified about the evidence. However, if you have a source indicating the experts specifically consider the evidence "worthless" (or any other word they consider it to be) then that would work too. ''''''