Maria del Rosio Alfaro was born on October 12, 1971, in Anaheim, California. She grew up in a city known for its theme parks and sunny weather. Alfaro's early life was marked by challenges. By the age of 13, she had started using drugs. As a teenager, she faced struggles that led her to become a drug addict. At 14, she began engaging in prostitution. By 15, Alfaro became a single mother. Over the next few years, she gave birth to four children. 

On June 15, 1990, Maria del Rosio Alfaro murdered nine-year-old Autumn Wallace in Anaheim, California. Alfaro was familiar with the Wallace family, having been a friend of one of the older sisters. On the day of the murder, Autumn was home alone, waiting for her family to return from work. Alfaro approached the house and asked Autumn if she could use the bathroom.

After entering the home, Alfaro took a knife from the kitchen. She then lured Autumn into the bathroom and attacked her, stabbing her 50 times. After the murder, Alfaro searched the house for valuables to steal. She later sold the stolen items for $240.

During a police interview, Alfaro confessed to the crime. She claimed that she was high on heroin and cocaine at the time. However, there was no drug test conducted on her immediately after the murder. Alfaro later changed her story multiple times, alleging that an unidentified man either forced her to stab Autumn or that he had driven her to the house. She refused to identify anyone involved. The investigation found that only members of the Wallace family and Alfaro's fingerprints were present at the crime scene.

Alfaro was tried and found guilty of first-degree murder, with special circumstances. The jury voted on her punishment, but they were unable to reach a unanimous decision about the death penalty at first. A second jury eventually sentenced her to death. In doing so, Alfaro became the first woman sentenced to die in the gas chamber in California. As of now, she remains on death row. The California Supreme Court upheld her sentence in August 2007.