Elizabeth Ann Duncan, often referred to as "Ma" Duncan, was born Hazel Lucille Sinclaira Nigh on April 16, 1904, in Kansas City, Missouri. Throughout her life, she had a tumultuous personal history, admitting in court to having been married ten times. She had a son, Frank, who became the center of her life, and a daughter, Patricia, who died at age 15. Elizabeth had a history of legal troubles, including arrests for operating a brothel in San Francisco and passing bad checks. Her deep attachment to her son Frank led to obsessive and controlling behavior, especially concerning his personal relationships.

In 1958, Elizabeth's son, Frank Duncan, a 29-year-old attorney, married Olga Kupczyk, a 30-year-old nurse, after Olga cared for Elizabeth during a hospital stay. Elizabeth strongly opposed the marriage, feeling threatened by Olga's presence in Frank's life. She harassed Olga at her workplace and attempted to undermine their relationship. When these efforts failed, Elizabeth devised a more sinister plan.​

Elizabeth approached two men, Augustine Baldonado and Luis Moya, offering them $6,000 to murder Olga. On November 17, 1958, Baldonado and Moya kidnapped Olga from her apartment in Santa Barbara, California. They drove her to a remote area along Highway 150 in Ventura County, where they beat and strangled her. Olga, who was seven months pregnant at the time, was then buried in a shallow grave.​

Suspicion quickly fell on Elizabeth due to her well-known animosity toward Olga and her erratic behavior following Olga's disappearance. Investigations revealed Elizabeth's attempts to annul Frank and Olga's marriage fraudulently. Baldonado and Moya were apprehended, and their confessions implicated Elizabeth as the mastermind behind the murder.​

In 1959, Elizabeth was tried and convicted of first-degree murder. Despite multiple appeals, her conviction and death sentence were upheld. On August 8, 1962, Elizabeth Ann Duncan was executed in the gas chamber at San Quentin State Prison. Her execution marked the last time a woman was executed in California before the U.S. Supreme Court's 1972 decision in Furman v. Georgia, which led to a temporary suspension of the death penalty nationwide.​