Two things would prevent that. First, HLNT was able to find evidence already that Humphries was not able to dispose of when he was ousted. For Walters to lie in the face of such evidence would be crazy insane, and he is not that at all. Humphries would have been more prone to stating Falsehoods, but as he has been to jail, he would be aware of what could happen if he was caught in another lie. In his case, he would more likely plead the fifth. Also, Walters had to give his Deposition before that of Humphries. In the depositions, questions and answers can lead to more questions, and Ted Max is sharp enough that he could spot evasiveness and misstatements very quickly. It's not to say that they might not try, but review of any evidence that may have been provided by Walters, if either did not tell the truth, it would come back to bite them in the posterior.