After the DNA match, Detective Goddard promised to obtain DNA samples from the other two suspects. He said the motel rooms had been cleaned before he had a chance to collect evidence and that the motel’s security footage had been lost.

Six weeks later, he called to say that the assistant district attorney, Ms. Montford, had declined to pursue the case. He referred to the strangulation mark on Ms. Borchardt’s neck as “a hickey” and said she had been “flirting” with the men in the car.

Last fall, Ms. Montford told her former sister-in-law, who was also a family friend of the Borchardts, that she did not believe Ms. Borchardt’s story.

The former sister-in-law recorded the conversation, in which Ms. Montford repeatedly describes the encounter with the third man as consensual, according to a transcript included in court filings. She said that the detective had seen video footage from the motel, but that “by the time they went back and got it, the hotel had already recorded over it.”

She also said the reason the detective did not collect evidence was that “once both parties say it’s consensual they’re not going to take any evidence out of that, other than his DNA.” Ms. Borchardt’s lawyers are exploring a potential defamation claim.

Finally, after repeated requests, Detective Goddard conducted a formal interview with Ms. Borchardt. He asked her to try to put herself in the minds of her assailants, the lawsuit said, repeatedly told her that her account was not what a jury would want to hear, and asked whether, when the older man was fingering her in the shower, he might have been trying to wash her.

Among the shifting explanations for why the case would not be prosecuted, according to the lawsuit: Ms. Borchardt’s head contusion did not have “bone splintering or fracturing” and the bruising on her neck “was not big enough.” It is not clear whether DNA from the other two suspects was ever collected or tested.