Tammy Homolka was Karla Homolka's 15-year-old sister, and as a "Christmas present" on Dec. 23, 1990, Karla Homolka offered Bernardo Tammy Homolka's virginity, according to ThoughtCo. At the Homolka family Christmas party, Karla Homolka served Tammy Homolka a drink spiked with an anesthetic Karla Homolka stole from her workplace, which was a veterinary clinic at the time.

When the rest of the family went to sleep, Bernardo and Karla Homolka covered Tammy Homolka's mouth with a Halothane-soaked cloth to ensure she was unconscious, and together, they sexually assaulted her. Meanwhile, Tammy Homolka choked on her own vomit, and since the drugs in Tammy Homolka's system were undetected in her autopsy, her death was ultimately deemed an accident, despite the chemical burn on her face.