On the night of September 14, 1984, 24-year-old San Diego Police Department officer Kimberly Sue Tonahill was killed while on patrol in Balboa Park. She and her partner, Officer Timothy J. Ruopp, stopped a vehicle that contained two men and two underage girls and planned to issue a citation for contributing to the delinquency of minors. During the encounter Tonahill began to pat down one of the men, identified as Joselito Cinco, who produced a handgun, pushed her away and shot her at point-blank range in the gap between her vest and armpit. Cinco continued firing as she fell, then shot Officer Ruopp in the head and fired additional rounds into both officers. Cinco then forced the two girls into the patrol car and fled the scene.

Cinco was later identified, arrested and charged with two counts of first-degree murder; he was convicted and sentenced to death. While on death row at San Quentin State Prison he later hanged himself. Officer Tonahill was the first woman in the San Diego Police Department to die in the line of duty.