Dr. Bennett Alston is the personal psychologist of murder victim Marnie Owens, a youth educator with an addiction to sex. Alston was found thanks to Marnie's brother Jordan when her addiction was revealed through one of her partners, Ethan Chance.
After Alston elaborated more of his treatment with Marnie, the sex club she went to was found, which led to Marnie's killer, Philip Montrose. Montrose ended up with a manslaughter verdict when he said Marnie's murder was an accident. (SVU: "Secrets")