Sorry, can’t link but there is a NY Post article and a Daily Mail article on this that shows the case may not be so clear cut. Prosecutor initially wasn’t going to charge but after the investigation changed his mind. Sister of deceased father alleges physical exams by prosecution shows two of the daughters are virgins contradicting their claims that they had group sex with their father. Father was no saint, he allegedly maced them for leaving the home messy.
The test would eliminate only vaginal sex. Dozens of stab wounds to the neck and chest bespeaks a great deal of rage. I wonder if all three contributed.