Theresa Jimmie Francine Knorr was born on March 14, 1946, in Sacramento, California. She was the younger of two daughters to Swannie Gay and James "Jim" Cross. Swannie had a son and a daughter from a previous marriage. Jim worked as an assistant cheese maker and eventually saved enough money to buy a home in Rio Linda. However, the late 1950s brought challenges for the family. Jim was diagnosed with Parkinson's disease, leading him to quit his job. This caused him to feel depressed, and he often took out his frustrations on his family. Swannie worked to support the family financially.

Theresa was very close to her mother. When Swannie died from congestive heart failure on March 2, 1961, Theresa was devastated. Following her death, Jim could no longer maintain the family home, so he sold it.

At 16 years old, on September 29, 1962, Theresa married 21-year-old Clifford Clyde Sanders. She met him a few months earlier and dropped out of high school right after the marriage. Theresa soon became pregnant and gave birth to her first child, Howard, on July 16, 1963. The marriage was difficult as Theresa was possessive and often argued with Clifford, accusing him of cheating. On June 22, 1964, during one such argument, she claimed he hit her. Although she reported the incident to the police, she chose not to press charges, and the case was dropped.

On July 6, 1964, the day after Clifford's birthday, they had another fight. During this argument, he told her he was leaving her. Enraged, Theresa shot him in the back with a rifle. She was arrested and charged with murder but pleaded not guilty, claiming self-defense. During the trial, she was pregnant with her second child. Despite conflicting testimonies about Clifford's character, Theresa was acquitted of the murder on September 22, 1964.

She gave birth to her second child, Sheila, on March 16, 1965. After Sheila's birth, Theresa began drinking heavily. She often went out to drink, leaving her children with a man named Estell Thornsberry, a disabled Army veteran she had begun dating. Their relationship ended when he discovered she was cheating on him.

In 1966, she met and married Marine Robert Knorr. They had four children together: Suesan, William, Robert Jr., and Theresa "Terry." The marriage faced its own challenges, as Theresa frequently accused Robert of cheating, leading to much strife. Eventually, Robert left her in December 1970, and their divorce was finalized in 1971.

Theresa married two more times. Her second husband, Ronald Pulliam, divorced her after only a year, believing she was unfaithful. Her last marriage was with Chester "Chet" Harris in August 1976, which also ended in divorce later that same year. 

Theresa Knorr abused her daughter Suesan for two years by chaining her to the dining room table. On July 16, 1984, Theresa uncuffed Suesan for a brief moment but handed her youngest daughter, Terry, a gun and threatened her to shoot Suesan if she moved. While the children were in the kitchen, a spoon dropped and startled Terry, causing her to accidentally pull the trigger and shoot Suesan. Instead of helping her bleeding daughter, Theresa became upset that Suesan's blood stained the carpet. She forced Suesan to stay in the bathtub for weeks, refusing to take her to a hospital. Eventually, Theresa gouged the bullet out of Suesan's body while she was unconscious, leading to an infection and sepsis.

Later, Theresa ordered her sons, Robert and William, to dispose of Suesan's body after putting her in trash bags and binding her. They drove her to Squaw Valley and set her on fire, believing she was dead. However, Suesan was still alive and her body was found the next day, classified as Jane Doe.

After this, Theresa shifted her focus of abuse to her other daughter, Sheila. In May 1985, she forced Sheila into prostitution to support the family. A few weeks later, Theresa accused Sheila of being pregnant and hog tied her, locking her in a closet without food or water. Although Terry sneaked her sister some food and drink, Sheila died from dehydration and starvation three days later. Theresa left Sheila's body in the closet for an additional three days before instructing her sons to dispose of it.

The boys put Sheila in a cardboard box and abandoned her body near Truckee-Tahoe Airport, where it was later discovered and classified as another Jane Doe. To cover up her crimes, Theresa ordered Terry to burn down their apartment a few years later. The fire did not destroy the evidence as planned, prompting investigators to reopen the cases.

Terry managed to escape her mother's abuse and eventually reported what happened to the police. This led to an investigation that linked Suesan and Sheila's deaths to Theresa. On November 10, 1993, Theresa was arrested in Salt Lake City, where she had been living under a different name.

Charged with two counts of murder, Theresa initially pleaded not guilty but later accepted a plea deal, sparing her from the death penalty. On October 17, 1995, she was sentenced to two consecutive life sentences. She is currently serving her time in California Institution for Women.