Katherine "Katie" Nevins (Elisabeth Moss) is the main villainess from "Baby Boom," episode 1.05 of Law & Order: Trial by Jury (airdate March 25, 2005). She is a live-in nanny who is also a practicing fashion designer.
As the episode progressed, Katie is revealed to have violent tendencies towards her young charges, which were connected to occurrences getting in the way of her designing. While serving as a nanny for the Rawlings family, Katie caught 4-year-old Kevin making a cape out of expensive fabric she was using to make a purse, and unleashed her anger by spanking Kevin so hard that she left welts on him. She later served as a nanny caring for Marissa Downey, and she unleashed her abuse on her as well, breaking her wrist after finding out she missed a deadline in her fashion class.
Six weeks later, Katie set up a meeting regarding a job interview, and later phoned Marissa's mother, Dr. Emily Downey, if she could return home so she could leave. Emily stated that she was busy with work and couldn't, which caused Katie to burst into tears and beg her to send someone to watch Marissa. After Emily hung up on her, Katie took her disappointment out on a crying Marissa; violently shaking her in a twisted attempt to quiet her--before slamming her on a wall, which killed her. Katie ended up arrested and charged with second-degree murder.
During her trial, the callous and evil Katie attempted to place blame on Emily, claiming that she believed Marissa was sick and when she told Emily, she was brushed off. She also stated that she called 911 regarding Marissa, and followed the operator's instructions to check the airway. However, Kibre gave a demonstration and reenactment of Katie calling 911 during her closing argument, while playing the call, which showed that Katie didn't check the airway; because the instructions were coming too fast and--more importantly--Katie knew exactly what was wrong with Marissa: her head was slammed down.
Katie was convicted of second-degree murder, but Judge Patel (a former legal aid attorney) felt that the jury's conviction was solely based on emotions and not facts, and he overturned Katie's conviction, allowing her to go free.