Caroline Darian and her two brothers were frantically moving their mother out of the family house that had effectively become a crime scene when she was interrupted by a call from the police saying they had something to tell her in person. It could not wait.

She was already shattered by the news that the father she always believed was loving and supportive had been arrested on suspicion that he drugged and raped her mother, and that he allegedly brought other men to join him in violating her for almost 10 years.

What, she wondered that day in November 2020, could there be left to learn?

What came next was a new shock, Ms. Darian testified on Friday in her father’s trial. Besides the thousands of photos and videos the police said her father kept of her unconscious mother being abused, the officers had discovered two photos of another woman asleep in bed, with the covers off and the lights on. It took Ms. Darian, who goes by a pen name she created after the accusations, a while to register that the woman was her.

“I realized right away I was drugged in that photo,” Ms. Darian, 45, testified before the criminal court in Avignon, France.

The question that still haunts her: “To do what?”

Prosecutors have not charged her father with drugging or sexually abusing her, which she suspects he did and which his lawyer says he denies. But he is accused of violating her privacy by “taking, recording or transmitting” a sexual image of her without her knowledge.

While it is clear that the undisputed victim at the center of this devastating family drama is Ms. Darian’s mother, Gisèle Pelicot, the entire family remains badly wounded and dogged by questions that perhaps will never be answered.