On Wednesday, 10 December 1969, 16-year-old Leona Larell Roberts worked her first day at a part-time job at the White Front Discount Store in Pleasant Hill. After her 1-5 p.m. shift, she drove to her boyfriend's apartment (749 Tormey Ave., Rodeo) where she planned to cook him dinner. At the time, Leona attended K's American Beauty College in Napa, where she also lived with her mother. Within 15 minutes of arriving at her boyfriend's apartment, a neighbor heard a girl scream. The neighbor called the sheriff and soon after heard someone running down the stairs at the back of the apartment house followed by the slam of a door from the direction of the downstairs apartment where Leona's boyfriend lived. When the boyfriend arrived, he saw Leona's red VW out front but did not find her inside the apartment. The apartment was dark and the back door was unlocked. He noticed scuff marks on the wall near the back door. He found that a pair of his pants had been removed from the bedroom closet and left on the living room couch, the belt missing. He noticed Leona's work smock crumpled on the couch. A sheriff's deputy arrived 30 minutes after the call. Another neighbor told the deputy of seeing a white male, about 25 years old, short blonde hair, acting suspicious. He walked several times from the front door to the rear of a blue station wagon before driving away.

On 28 December 1969, a man searching for driftwood on the beach at Bolinas Lagoon in Marin County found the nude body of Leona Roberts. It was later determined that a unique wristwatch was missing from the girl's wrist, but a Napa High School class ring given to her by a neighbor still remained on her finger. The tan dress she wore when last seen, along with two pairs of bell-bottomed pants, a blouse, a black purse and wallet, a key chain with car and house keys were also reported missing. There were marks on the wrists and ankles indicative of binding, but the coroner was unsure whether they occurred before or after death. The cause of death was reported as "due to viral infection of an unidentified species." It was also reported that there was "evidence of choking which could probably be linked to the virus." The coroner estimated that she had been dead 4-7 days (December 21-24) prior to recovery, and he theorized that she had been alive 10-14 days after her abduction. Articles reported the coroner's theory that Leona had been kept bound for a period of time, died as a result of the viral infection, and was disposed of by her abductor(s). Pathological and toxicological tests did not find any drugs or alcohol in her system.

Law enforcement agencies in Contra Costa, Marin and Napa all investigated the case in the initial days of her disappearance. Articles mentioned the recent abduction of 17-year-old Elaine Louise Davis from her Walnut Creek residence on 1 December 1969, her body later found 19 December 1969 near Lighthouse Point in Santa Cruz. Articles at the time stated that there was no indication that the Roberts or Davis cases were connected to the recent Zodiac activity. Author Robert Graysmith lists Leona Roberts as possible Zodiac victim #10 in his 1986 book. More information on the Roberts case can be found on Zodiac websites.