Kristin Margrethe Rossum was born on October 25, 1976, in Memphis, Tennessee. She was raised in Claremont, California, where she was the oldest child of Ralph and Constance Rossum. Ralph worked as a professor, and Constance was employed at Azusa Pacific University. Kristin had two younger brothers.

In 1991, when Kristin was about 14 years old, her family moved to Virginia. This move was due to her father's new job as President of Hampden–Sydney College. Kristin attended St. Catherine's School, a private all-girls school in Richmond. During her time there, she began experimenting with alcohol and cigarettes. She also tried marijuana but found it did not affect her much. In 1992, she started using methamphetamine.

By 1994, Kristin and her family returned to California. She enrolled part-time at the University of Redlands and moved into a dorm on campus. However, she soon left school due to a relapse in her drug use. After working towards overcoming her addiction, Kristin began a relationship with Greg de Villers. This relationship encouraged her to continue her education, and she enrolled at San Diego State University. She graduated with honors in 1998.

After earning her degree, Kristin worked as a toxicologist at the San Diego County medical examiner's office. She married Greg de Villers in 1999. In the following year, she began an affair with her boss, Dr. Michael Robertson. 

On November 6, 2000, Kristin Rossum called 9-1-1 and reported that her husband, Gregory de Villers, had committed suicide. When the paramedics arrived, they found de Villers unresponsive on the couple's bed, surrounded by rose petals. He was pronounced dead at the hospital shortly after. Rossum claimed that he had killed himself, but his family disagreed and insisted he was not suicidal.

Just one month after the death, both Rossum and her boss, Dr. Michael Robertson, were fired from their positions at the medical examiner’s office. Rossum was let go for concealing her methamphetamine addiction, while Robertson lost his job for enabling her substance abuse. With potential conflicts of interest, the medical examiner's office decided to have de Villers' autopsy performed at an outside lab in Los Angeles. The autopsy revealed that he had a lethal amount of fentanyl in his system.

As the investigation progressed, authorities learned that Rossum had called her husband’s workplace to say he would not be coming in on the day he died. During questioning, she claimed her husband had been depressed prior to his death, but her family also spoke about his distress that night, noting he had been drinking.

On June 25, 2001, nearly seven months after Martin's death, Kristin Rossum was arrested and charged with murder. The trial began with the prosecution arguing that she had killed her husband to prevent him from revealing her affair and her drug use. The defense countered by asserting that de Villers had taken his own life. In court, evidence included a store receipt showing that Rossum had bought a rose around the time she claimed to have been at home caring for him. Rose petals were found at the scene, leading to conflicting narratives about whether they were placed there by de Villers or if Rossum had prepared the scene to suggest a suicide.

On November 12, 2002, Rossum was found guilty of first-degree murder. She was sentenced to life in prison without the possibility of parole and a $10,000 fine. Following her conviction, she was transferred to a correctional facility in Chowchilla, California. In 2006, a jury ordered her to pay over $100 million in damages to de Villers' family in a wrongful death lawsuit, which was later reduced.

Kristin Rossum's case has continued to draw attention in the media, being featured in various true crime documentaries and books. As of now, she remains incarcerated for her crimes.