Betty Broderick, who became infamous for the 1989 killings of her former husband and his new wife in a case that shocked the country and inspired movies and books, has died at the age of 78 while still serving a life sentence.

Representatives from the California department of corrections and rehabilitation confirmed to NBC News that Elizabeth A Broderick was moved from the California prison where she had been transferred to a medical center on 18 April. She died on the following Friday.

The medical examiner’s office initially determined the cause of death to be natural causes, though the San Bernardino county coroner will carry out a formal investigation, according to NBC.

Broderick became nationally recognized after fatally shooting her ex-husband, Dan Broderick, and his new wife, Linda Kolkena, on 5 November 1989. In 1991 she was found guilty of second-degree murder in connection with their deaths and received a prison sentence of 32 years to life.

Betty and Dan Broderick married in 1969 and had four children together. During the early 1980s, Dan began a relationship with Kolkena, a former flight attendant he had hired as a legal assistant while his marriage to Betty was deteriorating.

Although Dan denied the relationship when Betty first became suspicious, he later separated from her and filed for divorce in 1985. The divorce proceedings involved disputes over selling the family residence and determining custody arrangements for their four children. Dan ultimately received custody, while Betty retained visitation rights.

The fatal shootings occurred on a Sunday morning, reportedly after Betty Broderick received a letter from her former husband’s attorney that warned she could face contempt-of-court charges if she continued harassing and threatening her ex-husband and his wife. She stated during her trial that the letter ignited her anger “like a fuse”.

Broderick later went to the Hillcrest residence and entered using a key she had taken from her daughter weeks earlier. She quietly climbed the stairs to the bedroom and opened fire on Dan and Linda Broderick with a .38-caliber revolver. Both victims were shot three times and died from their injuries.

In February 1992, Broderick was moved to the California Institution for Women. She was reportedly serving a life sentence with the possibility of parole at the time of her death.

Rhett Broderick, the youngest of the couple’s four children, told the San Diego Union-Tribune that his mother had fallen in prison several weeks earlier and fractured some ribs. He said she later developed an infection that progressed into sepsis, from which she could not recover.

He also said that he and two of his siblings traveled to Chino and spent time with their mother before she died. “She passed away from natural causes with three of her children at her bedside, and the other was FaceTiming,” he said, adding: “We were all able to come and be with her.”