henry rayhons , 78 , is preparing to stand trial in iowa for sexually assaulting his wife donna lou rayhons .
suffering from dementia and alzheimers , she had been moved into a nursing home by her daughters from a previous marriage last year .
doctors had told rayhons that his wife of seven years was no longer mentally capable of legally consenting to have sex .
he ignored the request and charges were filed against him days after his wife died last august .
rayhons faces 10 years in prison if he is found guilty of sexual abuse charges .