Dr. Cheng was the colleague and brief girlfriend of sound engineering expert and anti-authoritarian Merritt Rook. Due to the loss of his wife and daughter, she agreed to a date with him at a nighttime music club where a friend of his was performing jazz.
As she would later tell the police, Rook heard one of the songs he and his wife composed together when she was still alive and playing her own music. Even to Cheng's sorrow, the memories from Rook's traumatic past came flooding back, and he ran out of the night club with a newfound sense of vigilantism. That would be revealed to be the stressor for Rook's campaign and criminal competition with the police and justice system. (SVU: "Authority")