Karl Francis Werner was born on May 12, 1952, in Marlborough, Massachusetts.

On August 3, 1969, the bodies of 14-year-old Debra Gaye Furlong and 15-year-old Kathie Reyne Snoozy were discovered in southern Almaden Valley. The girls had gone to picnic earlier that day. Investigators found their fully clothed bodies in a wooded area that overlooked their homes. They noted that neither girl had been sexually assaulted. Medical experts suggested the girls were likely killed at a different location because there was little evidence of blood at the scene.

The Santa Clara County Medical Examiner, Dr. John E. Hauser, examined the bodies. He reported that both girls had suffered numerous knife wounds. Kathie Snoozy had more than 200 wounds, while Debra Furlong had over 100. Most of the wounds were on the upper parts of their bodies, and neither girl showed signs of fighting back against their attacker. Dr. Hauser stated that in his career, he had never seen a case with such a high number of knife wounds.

On April 11, 1971, Kathy Bilek, an 18-year-old girl, visited a park called Villa Montalvo in Saratoga. She planned to read and watch birds in a quiet area. The next day, her father found her body during a search by Santa Clara County Sheriff's deputies. Kathy Bilek had been stabbed 17 times in the back and 32 times in her chest and stomach. The killer avoided stabbing her breasts.

After Kathy's murder, a maintenance worker at the park recognized the assailant. He described the man as "a little odd" and identified him as Karl F. Werner, who was a graduate of Oak Grove High School and a student at San Jose City College. Investigators connected Werner to the earlier murders of Furlong and Snoozy, labeling Kathy Bilek's case as similar to theirs.

Police had previously considered Werner a suspect in another knife attack on a woman. They obtained a search warrant and found the knife he used to kill Kathy Bilek at his home. In September 1971, Karl Werner confessed to killing Debra Furlong, Kathie Snoozy, and Kathy Bilek. As a result, he was sentenced to life in prison.

Initially, police suspected that a serial killer known as the Zodiac was involved in the murders of Furlong and Snoozy. However, later investigations revealed that Werner had lived in Marlborough, Massachusetts, during some of the Zodiac's crimes. Werner was imprisoned at the California Medical Facility in Vacaville and died in 2015.