Dr. Susan Hillridge is one of the two main villainesses, along with Carla Dantini, from CSI episode 1.21, "Justice Is Served." She is the villainess from the episode's main plot, which involves the death of a jogger, Terry Manning.
She was played by Alicia Coppola.
Susan Hillridge was a nutritionist who suffered from porphyria, a genetic blood disease which affected her physical health as well as her mental state. After failed attempts to counteract the disease, Susan resorted to serial killing; murdering joggers and harvesting their healthy organs. She had her dog attack joggers in different states, doing so by going for their throat, and she would cut out their livers, hearts, and spleens. Susan committed these murders in different states (mostly Mountain States) and had a different dog each time.
After acquiring their organs, Susan would ground them into powder and consume them as protein shakes. The villainess was arrested for the murders, but before she was taken away, the evil Susan revealed that she had a fresh shake in her fridge. It is assumed that Susan died of the disease while in prison.