Dr. Nora Selsky (Nicole Shalhoub) is the main villainess from "Bits and Pieces," episode 6.05 of Elementary (airdate May 28, 2018). She is a researcher for the NYC Department of Health.
Selsky interviewed a woman named Wu, who was the student girlfriend of teacher Eric Russo, as she was dying from H7N5, a rare bird flu disease. After Wu informed Selsky that Eric contracted the disease, Selsky checked out Eric and realized that he was asymptomatic; having become the first to fight off the disease and developed an immunity to it. She approached Eric in an attempt to use his antibodies to develop a vaccine that would be worth millions, but when Eric refused, she resorted to murderous means to achieve her lucrative goal.
Selsky killed Eric and dumped his body at a crematorium, but not before getting the necessary organs she needed for the vaccine. Unfortunately for the villainess, Eric's body was donated to a tissue bank, with Kareem Ludlow and Victoria Garvey receiving Eric's skin graft and catching the deceased's disease. After learning about the two graft recipients, the evil Selsky killed both of them, doing so to cover up her actions. She used her pass from a hospital she once worked at to gain access to each of her victim's homes, under the false claim that she had a cure for their illnesses. In actuality, Selsky was injecting her victims with a lethal dose of potassium chloride, and she burned the bodies afterwards.
Joan Watson and Marcus Bell were on the case after Sherlock Holmes ended up with Eric's head, and it was Selsky's story about her research that ended up revealing her as a greedy serial killer. Joan and Marcus confronted the villainess at her lab, with Selsky denying everything and threatening to call her lawyer. However, Marcus revealed that a search of Selsky's former workplace uncovered a spleen belonging to Eric in her freezer, and after this, Selsky was arrested (off-screen) for the murders.