Transcript for Exclusive: Woman Says Dennis Hastert Abused Her Brother in High School

We turn to the ABC news exclusive. Reaction pouring in after our interview, a family breaking its silence with allegations against Dennis Hastert. A onetime student at the school where Hastert taught and coach. Saying Hastert sexually abused their brother. What he wrote to their loved one in the yearbook. Reporter: Tonight, one of Hastert's alleged victims identified. This young man, Steve reinboldt, the student manager for Hastert's high school wrestling team, who Hastert called in that 1970 yearbook inscription, his great, right hand man. He damaged Steve, I think, more than any of us will ever know. Reporter: Speaking publicly for the first time, reinboldt's sister Jolene says her late brother revealed what she called the dark secret of abuse when he told her he was gay. I asked him, when was your first same-sex experience? He looked at me and said that it was with Dennis Hastert. And I just, I know, I was stunned. I said, why didn't you ever tell me, Stevie? He was your teacher. Why didn't you ever tell anybody? He just looked at me and said, who is ever going to believe me in this town? Who is ever going to believe me? Reporter: Hastert became a kind of father figure for her brother, she says. As a member of an explorer's troop run by Hastert, reinboldt was among a handful of young men Hastert took to the Bahamas, seen in these photos reinboldt took of the boys and Hastert relaxing. Here was the mentor, the man who was, you know, basically his friend, who was the one who was abusing him. Reporter: Steve reinboldt died of A.I.D.S. In 1995. His sister says she confronted then-congressman Hastert when he showed up unexpectedly at the funeral home. He just stood there and stared at me, and then I just continued to say, I want you to know that your secret didn't die in there with my brother. And I want you to remember that I'm out here, and that I know. Reporter: Then two weeks ago, she says, the FBI showed up at her door to ask about her big brother Steve and tell her Dennis Hastert was about to be indicted. There are no words to describe what it felt like to, you know, it's just like, Stevie, we've done it. It's going to happen. We got him. Reporter: His sister says she nor her brother ever asked for money. And the speaker has not responded to our request for meant. Why did she go on the record now? She says she's going public in the hope that other alleged victims can come forward as we

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