Sergeant Koeller was shot and killed after surprising burglars at Dandy's Mens Shop, at the northeast end of the Northland shopping center on West Florissant Avenue and Lucas and Hunt Road. Investigators believe he was surprised from behind as he got out of his patrol car. His radio microphone was still dangling out of the open car door and his revolver was not found at the scene. Indications were that he struggled with his assailant before being shot once in the neck. While he was detaining two of the suspects a third suspect came up from behind and started to struggle with Sergeant Koeller. During the struggle the suspect shot him in the neck, before all three fled the scene.

A fingerprint lifted from the scene produced a suspect in Ohio three years later but he was not convicted. The shooter was arrested in Illinois, confessed to the murder, and sentenced to two life sentences.

Sergeant Koeller joined the police department in 1970, serving for 17 years. He was promoted to sergeant in 1979 and became the watch commander for the midnight shift in September. Interred: St Charles Memorial Gardens, St Charles, MO.