Sabrina Erdely, center, enters the federal courthouse in Charlottesville where she and Rolling Stone magazine are being sued for defamation by a University of Virginia administrator. (Ryan M. Kelly/AP)

In emotional testimony in the federal courthouse here Saturday, former Rolling Stone writer Sabrina Rubin Erdely told the jury about the phone call that led her to realize that the story she had written about a horrific sexual assault at a University of Virginia fraternity was falling apart at the seams.

The story Erdely wrote for the magazine in November 2014, “A Rape on Campus,” created shock waves across the country with its description of a brutal gang rape of a freshman identified in the story only as “Jackie.”

Erdely, who is being sued along with the magazine for defamation by U-Va. administrator Nicole Eramo, had interviewed Jackie many times and believed her story. And she had interviewed friends of Jackie’s whom she also found believable.

[Rolling Stone reporter said she believed ‘Jackie’ and felt ‘scared for her’]

On Saturday, she testified that on a reporting trip to the university, she and Jackie had walked by the fraternity house where the rape allegedly took place and that Jackie had visibly recoiled when they neared it.

ABC News interviewed Nicole Eramo, the former University of Virginia administrator who is suing Rolling Stone magazine over a November 2014 story about a sexual assault. That story was discredited. (ABC News and 20/20)

“Her face had this look of, it was like terror and anger and fear.” Erdely said. “It was like she was frozen in this terrified mask.”

Erdely also interviewed friends, experts on sexual assault and university administrators for her story, but she did not reach out to the alleged attacker because, she said Saturday, Jackie had expressed so much fear for her safety and worried about what might happen to her or what he might do.

Soon after the story published, a number of Jackie’s claims were being called into question, Erdely said, and she and the editors at Rolling Stone were preparing a statement that said they stood by their article and the reporting.

Erdely reached out again to Jackie and spoke with her early in the morning of Dec. 5, 2014. She said she asked Jackie if she had gone to the police now that the story had come out to report the crime and that Jackie responded that it was not the right time.

“I was a little surprised,” Erdely told the court. “A couple of other things struck me as odd. . . . I was getting a little hinky feeling.”

Erdely says that for the first time, Jackie expressed doubt about whether her alleged assailant was in the fraternity she had said he belonged to.

“I was just so startled. . . . Here she was saying in such a casual way, ‘Oh yeah, maybe he wasn’t in Phi Psi.’ ”

Worried about the doubts Jackie was expressing, Erdely posed direct questions to her. The reporter’s notes from that phone call were shown to the jury.

Did he rape you at the Phi Psi house?

No.

Did he orchestrate your rape?

Yes.

Did it happen the way you told me it did?

Yes.

Erdeley said she then told Jackie on the phone that she wanted to work with her to look up additional information about her alleged attacker online. They searched but were unable to find anything. For Erdely, the doubts quickly mushroomed.

“When I got off the phone, I felt like the ground had shifted from under my feet,” Erdely said. “The person I had talked to was not the person I was familiar with from my story. I felt that she didn’t have credibility anymore, which meant that we couldn’t stand behind anything that she had given me.”

Wiping away tears, Erdely confirmed that she left a voice mail with Jackie telling her that if she didn’t believe in her story, she should not go to the police.

She then drafted an email to her editors explaining that she no longer had faith in Jackie’s story and telling them it should be retracted. The subject line read simply: “Our worst nightmare.”