WALTERBORO, S.C. — Alex Murdaugh didn't help his defense when he took the stand at his trial for the murder of his wife and son, three jurors said Monday.Murdaugh's testimony only managed to cement what they were already thinking — that he easily lied and could turn on and off his tears at will, the jurors said on the NBC Today show.The key piece of evidence in finding the lawyer guilty, they said, was a video on his son’s cellphone that was shot minutes before the killings at the same kennels …