Los Angeles County will retest about 4,000 DNA samples connected to criminal cases after discovering that it had been using potentially defective test kits to collect evidence for the past several months, Sheriff Robert Luna said in a statement this week.
The kits were “prone to intermittently poor performance,” the sheriff said on Wednesday, and were used on thousands of samples from July 2024 through February 2025 despite the manufacturer of the tests having informed the Los Angeles County Sheriff’s Department in an Aug. 28 letter that the tests could lead to incomplete results, the sheriff said.
The department was still trying to determine how many cases could have been affected by the faulty tests.
According to the statement, the department was not aware of the letter until Monday, when a supervisor with its Scientific Services Bureau realized that it had been sent to a person who was no longer employed by the Sheriff’s Department. The department has begun an internal investigation, the sheriff said.
“The Scientific Services Bureau is actively assessing how many cases may have been impacted and to what degree,” Sheriff Luna added, noting that the faulty tests would also affect other law enforcement agencies, as well as the Los Angeles County District Attorney’s Office.
In a statement posted to social media, the Los Angeles County Public Defender, Ricardo D. García, said that the use of the faulty kits had a “far-reaching impact on countless pending and adjudicated cases.”
He added, “This kind of negligence is a violation of due process and further erodes trust in the entire criminal legal system.”
The Sheriff’s Department did not supply a copy of the letter or the name of the test kit manufacturer. It also did not provide further information about the employee who first received the letter, nor when the employee had left the department. The Los Angeles County Sheriff’s Department, which has about 18,000 employees, says it is the largest in the nation.
“Based on the information provided by the DNA testing kit manufacturer, the use of the affected kits may have led to incomplete or suboptimal results but is not likely to have falsely identified any individual,” Sheriff Luna said in the statement. The department plans to retest the approximately 4,000 samples, he added, though he acknowledged that “certain samples may not be able to be retested due to their limited sample size.”
Nathan Hochman, the Los Angeles County district attorney, said in the statement from the Sheriff’s Department that his office was working to “assess the scope of the situation” so that anyone affected could make informed decisions about their cases.
“We will follow the facts in whichever direction they take us on any individual case and make decisions that are in full accordance with the law on how to remedy any particular situation that requires such remediation,” Mr. Hochman said.
His office did not immediately respond to a request for additional information about the faulty tests on Thursday.
Defective DNA tests, or those that are misused, can delay investigations and sometimes, implicate innocent people. One 2018 study showed that crime laboratories were likely to implicate an innocent person in a hypothetical bank robbery when they relied on DNA testing. Human errors have also led to major mistakes involving DNA evidence used in criminal cases.
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