David Westerfield was born on February 25, 1952. He grew up in a suburb of Los Angeles, California. He graduated from James Madison High School. After finishing high school, he became self-employed as an engineer. Westerfield held several patents for medical devices, showcasing his skills and creativity in engineering.

At the time of his later trials, Westerfield was 49 years old and had no criminal record. He was divorced and was a father to two college students. Westerfield lived in a home that was two houses away from the van Dams, a family with three children. He owned a luxury motorhome, which he used for weekend trips.

In the days leading up to a significant event, Westerfield had interacted with the van Dam family. About three days before the disappearance of seven-year-old Danielle van Dam, he purchased Girl Scout cookies from her and her mother, Brenda. During this visit, he invited them into his home. Brenda noticed that Westerfield's kitchen was being remodeled and asked to see the progress.

On the evening of February 1, 2002, Danielle van Dam went missing from her home in Sabre Springs, California. Her parents called the police the next morning after discovering she was not in her room. A massive search began immediately, involving hundreds of volunteers looking in deserts and remote areas. The search continued for weeks, and on February 27, 2002, searchers found Danielle’s body in Dehesa, California.

David Westerfield, a neighbor, became a suspect after traces of Danielle's blood were found in his motor home. He had been seen by witnesses on the night of her disappearance and had gone on a trip in his motor home shortly after she went missing. Westerfield was arrested on February 22, 2002, as evidence against him mounted.

During the trial, the prosecution presented forensic proof, including blood stains from Danielle on Westerfield's clothing and in his motor home. There were also hairs from the van Dam family's dog found in Westerfield’s laundry and fibers matching Danielle’s found in multiple places associated with him.

Westerfield’s defense attempted to argue that the police had rushed to identify him as the killer and that evidence could have belonged to other suspects. However, the jury found him guilty of first-degree murder, kidnapping, and possession of child pornography on August 21, 2002.

In the penalty phase, evidence of Westerfield's past behavior also came to light. A niece testified that he had inappropriately touched her when she was young. On September 16, 2002, the jury recommended the death penalty, which was officially sentenced by Judge William Mudd in January 2003. Westerfield is currently imprisoned at High Desert State Prison and remains on death row, although executions were paused in California.

The van Dam family sued Westerfield and received a settlement, which prevented him from profiting from his crimes. Reports later revealed that a plea deal was close before the discovery of Danielle’s body, which sparked controversy. Over the years, Westerfield maintained his innocence, but an outside letter claiming responsibility for Danielle's murder was dismissed by authorities as not credible.