Medical Detectives

In 1992, in a rural Canadian community, Dr. John Schneeberger is accused of sedating and sexually assaulting one of his female patients and his step daughter. DNA tests demonstrate that the doctor is innocent, but the female patient still insists that he sedated and raped her. On three occasions, blood was taken from the doctor's arm for DNA testing, and each time, the results exonerated Schneeberger. Seven years later, a private investigator takes lip balm from Schneeberger's car, has it DNA-tested and the results were a match to the perpetrator. So, how did Dr. Schneeberger trick earlier investigators?