Leah Moore (Stacey Carino) is the main villainess from "Dead Weight," episode 7.07 of Rizzoli & Isles (airdate July 18, 2016). She is a chemist and a former employee at a lab tech company; having lost her job due to her drug use.
After her firing, Leah checked into rehab, where she met fellow addict Robert Hall. The two of them decided to work together and sell drugs, with Leah acting as a mentor of sorts to Robert. However, Robert decided that he no longer needed Leah's expertise and went on his own, leaving Leah enraged and vengeful.
Leah then planned to kill Robert, using her scientific knowledge to eliminate her former partner. The villainess retrieved canisters of human fat that were illegally discarded by villainous surgeon Verusca Vela, and used the contents to create an explosive that she placed inside Robert's water bottle. In the beginning of the episode, Leah's makeshift murder weapon activated while Robert was riding his bike, killing him instantly.
The nature of the death caused Frankie Rizzoli Jr. to believe that spontaneous combustion killed him, but Maura Isles came to the correct conclusion after finding information on Leah, including that she worked in a building right next to Vela's. While Korsak and Frankie (among others) searched Leah's home, where her materials were, the evil Leah ended up found by Maura, who chased the villainess and engaged in a makeshift fencing battle with her. After she was subdued by Maura, Leah was arrested for Robert's murder.