Lauren Cooper

Lauren Cooper was the main villainess from "Signature," episode 9.12 of Law & Order:  SVU.

She was played by Erika Christensen, who famously played Madison Bell in Swimfan.

Lauren Cooper was an FBI agent who spent years tracking a serial killer named Larry Moore, nicknamed "The Woodsman," originally working with her mentor, Dr. Tillman. After Tillman committed suicide, Lauren continued her pursuit, and was called to aid Benson and Lake on their search. All the while, Lauren began succumbing to the emotional stress.

Lauren had actually tracked Moore down and attempted to force him to reveal the location of his latest victim. When Moore refused, Lauren shot and killed him, and kept the shell casing as a trophy. As a form of symbolism, Lauren used the gun that Tillman used to kill himself, having received the gun from Tillman's widow as something to remember him by. She and Benson eventually find Moore's victim alive, but she eventually dies due to the severe amount of damage done to her.

Lauren's reveal came later on, when video evidence led to her being fingered as Moore's killer. She is later arrested and interrogated by Benson, who asks Lauren if she and Tillman were actually lovers. An infuriated Lauren denies the claim, stating she killed Moore for all the women he hurt. Lauren is later charged with the murder, but the charges are dropped due to lack of evidence. After Novak refiled the charges, Benson and Lake learn the truth about the gun Lauren used to kill Moore, leading to the duo heading to Lauren's apartment to arrest her again. Lauren finally confessed everything, and Benson stated that Lauren will face a more lenient sentence based on Moore's history. Even with that, Lauren refused to turn herself in, and stated that those who hunt monsters should avoid becoming one, right before she took the gun and committed suicide.