For the first time in the U.S., evidence derived from next generation sequencing (NGS) has been accepted in a court of law. In this specific case, NGS testing was used to establish the location of the crime scene, as well as to help determine the circumstances of the violent assaults and murders.
Analyzing DNA using capillary electrophoresis is traditional, and still considered the “norm” for many forensic and crime laboratories. However, NGS technology has been making waves ever since it first burst onto the scene. Initially seen as a win for the clinical research field, the decreasing cost of NGS over time—in combination with the rise of investigative genetic genealogy—has made the technology an increasingly popular choice for forensics.
Due to its newness, though, NGS had not been through and approved by the U.S. court system. Now, the solving of the murders of two homeless women in Kern County, California has changed that—mostly likely altering the entire forensic DNA landscape in the process.
“NGS is a groundbreaking advancement in DNA evidence testing. I’m proud of our Kern Regional Crime Lab for pioneering this state-of-the-art method and introducing it for the first time in a U.S. trial,” said District Attorney Cynthia Zimmer. “This technology is a game-changer for solving crimes, as the extensive information it provides will lead us to even more significant discoveries.”
Two murders
On Oct. 12, 2020, Marilyn Cuervo was found deceased in a dirt field behind the Desert Star motel off in Bakersfield, Calif. It was quickly determined she has suffered significant blunt force injuries that resulted in her death.
Less than a year later, on July 26, 2021, officers from the Bakersfield Police Department responded again to the Desert Star motel, now abandoned. There, they found the body of Crystal Hernandez, immediately observing that she had suffered fatal blunt force injuries similar to Cuervo.
The officers were correct, as physical evidence later showed both women suffered nearly identical violent assaults with the use of blunt force instruments.
The investigation of both homicides led to Adrian Chavez, who police were able to confirm had been seen with both Hernandez and Cuervo near the time of their murders. Additionally, DNA and fingerprints recovered from the crime scene and bodies were linked to Chavez.
Part of the forensic testing involved the use of Verogen’s MiSeq FGx Sequencing System, a next-generation sequencer. Before the testing, the Kern Regional Crime Lab validated and implemented the sequencing system to allow for in-house NGS testing.
“NGS DNA testing enables the Kern Regional Crime Lab to test 152 genetic markers (forensic loci) in a single sampling of an evidence item compared with the previous method, which identified 24 genetic markers,” the lab explained.
The lab says the NGS testing was used to establish the location of the crime scene in Hernandez’s murder, as well as to help determine some of the circumstances of her violent assault and murder.
This case officially marks the first time NGS DNA testing was introduced as evidence in a jury trial in the U.S. Following an extensive pretrial admissibility hearing, the trial court deemed NGS to be reliable, and that the technique has gained general acceptance in the scientific field.
On Jan. 22, 2024, a Kern County jury found Chavez guilty of the first-degree murders of both Cuervo and Hernandez. The jury also found the defendant guilty of the special circumstance of multiple murders. Sentencing is scheduled for Feb. 21. Chavez faces a maximum sentence of life in prison without the possibility of parole.