Emily McCooper is the villainess from "Gone," episode 7.16 of Law & Order: SVU.
She was played by Maggie Siff.
Law & Order: Special Victims Unit
Emily McCooper was a newly hired court officer and the revealed lover of Nicky Pratt, who (along with Jason King and Doug Waverly) was facing charges for the rape and murder of Canadian student Jennifer Durning. Emily's relationship with Nicky began as she left from her job one day, with Nicky making remarks about how good she looked in the uniform, which led to a sexual encounter.
Afterwards, Emily planted a bug in Judge Elizabeth Donnelly's office, doing so to find out important details in Doug and Nicky's trial. One detail was that Jason became a witness against Doug and Nicky, and following this, the evil Emily kidnapped Jason and drove him to a business owned by Doug's father. The villainous conspirator later traded in her old car (an '89 Acura; which she drove Jason in) for a new Mercedes, which Emily insisted was a gift and not a payoff.
Emily's reveal came when Stabler showed her the receiver to the bug, which was in Emily's locker. After unsuccessfully denying her role, Emily confessed everything to Stabler, including where she took Jason. Her actions led to Doug and Nicky killing Jason to keep him quiet.