Steven Kellerman was the biological father of Sarah Brown. He worked with her mother, Andrea Brown, and had an affair with her, which ended soon after it began. Andrea had kept the fact that he had a child with her from him and he didn't know about Sarah until after she was killed. He loved Andrea, but didn't want to come between her and her husband. According to Steven, he had a brother that died of Tay-Sachs. (SVU: "Mercy")