Hidden-camera footage released this week shows a Berkeley materials engineer calmly adding a substance to a colleague's desk water bottle — a substance later confirmed as cadmium, a carcinogenic heavy metal, at concentrations reaching 3.5 million times the federal drinking water limit. Seven years after that footage was recorded, the man responsible is walking away with his felony conviction cleared from standard employer searches.
The case has exposed a structural tension inside California's criminal justice system: completing a probation term legally entitles a convicted poisoner to have a felony removed from routine employment background checks, regardless of how severe the original offense was or how permanently the victim has been affected.
18 Months of Slow Poisoning Before Anyone Knew What Was Happening
Rong Yuan, a metallurgist who holds a doctorate in materials science from the University of California at Berkeley, joined Berkeley Engineering and Research in January 2017. The firm — a forensic engineering consultancy that provides expert witness services to law firms and government agencies — was also the workplace of David Xu, who had been employed there since 2009 as principal engineer and laboratory director. Xu held his own UC Berkeley doctorate, with specialization in the mechanical behavior of materials. According to The San Francisco Standard, both earned their advanced degrees from the same Berkeley research lab.
Beginning in late 2017, Yuan's health began to unravel. She experienced episodes severe enough to require emergency care and noticed a recurring, unexplained taste and smell coming from food and beverages left unattended at her workstation. The symptoms — vomiting, hair loss, and systemic illness — accumulated over approximately 18 months before their cause was identified.
When Yuan fell seriously ill, her parents flew from China to the United States to look after her, before either of them knew she was being poisoned. Her mother cooked with water from the same bottle Yuan had been bringing home from the office. Both parents subsequently became ill, and cadmium was detected in blood samples from Yuan and both her parents. Her father, who was among those poisoned, later died of heart failure. Her mother continues to cope with serious cardiovascular and metabolic health complications that Yuan attributes to the cadmium exposure.
It was Yuan who identified the source. Growing suspicious, she installed a hidden camera at her workstation. The footage she captured shows Xu calmly adding a substance to her water bottle. She handed the recording to Berkeley police, who launched an investigation and arrested Xu at his Lafayette home in March 2019. She released that same video to the public this week — seven years later — precisely as Xu moved to erase the legal record of what he had done.
A Plea Deal That Even Shocked the Judge
Prosecutors originally charged Xu with premeditated attempted murder for what he did to Yuan, along with two felony counts of poisoning for the cadmium found in her parents. Together, the charges carried the possibility of a life sentence in state prison. In September 2023, under former District Attorney Pamela Price, Xu entered a no-contest plea to a single count of felony poisoning — a plea that carries the legal weight of a conviction but does not constitute a formal admission of guilt — and the remaining charges were dismissed.
The original agreement called for one year of probation and credit for one day served. The judge who handled Xu's sentencing in March 2024, Kimberly Colwell, made clear the deal troubled her. She described the arrangement as "extremely generous, considering everything in this case" and extended his probation from one year to two, also instructing him directly never to handle any poison again. Price, who won office in 2022 on a platform of reducing incarceration, was recalled by Alameda County voters the following year, with critics frequently citing the leniency of plea deals like this one.
California Law Left the Victim No Way to Block the Expungement
Under California Penal Code Section 1203.4, a person who successfully completes all conditions of probation is entitled to petition a court for dismissal of the underlying conviction. Courts have held that judges are legally required to grant such petitions once all conditions are met, unless the crime falls within a defined list of exclusions. Poisoning is not on that list. Xu completed his probation in March 2026 and filed his petition in July.
The hearing took place on October 12 before Judge Pelayo Llamas at Alameda County Superior Court. Assistant District Attorney Priscilla Vuong argued against granting the petition on the prosecution's behalf. Yuan attended and delivered a victim impact statement to the court. Xu's attorney participated by video; Xu himself did not appear. The ruling went in Xu's favor.
In her statement, Yuan spoke about the deaths and suffering her family had endured. "My father suffered years of declining health and died without seeing justice," she told the courtroom. Yuan said she does not fault Judge Llamas, acknowledging that he followed what the law required of him — but that understanding has not softened what she describes as an ongoing institutional failure to protect victims of serious crimes.
What Expungement Actually Means — and What It Doesn't
The word "expungement" can imply a total erasure, but California's dismissal process is significantly narrower. Xu's arrest and conviction remain fully visible to law enforcement and can be used against him in any future criminal proceedings. What changes is the civilian landscape: the dismissal removes his obligation to disclose the felony conviction to private employers conducting standard pre-employment background checks.
That outcome is precisely what Yuan feared most — that someone hiring Xu would find nothing. She released the spy-camera footage as a deliberate counterweight to the legal erasure, calculating that what a background check can no longer surface, an internet search very well might. Yuan says she continues to suffer liver and gastrointestinal damage she attributes to the poisoning. She suffered a heart attack in 2023 and says persistent health problems prevent her from working full time.
The Alameda County DA's Office Responds
Alameda County District Attorney Ursula Jones Dickson, who took office in February 2025 following Price's recall, confirmed her office had formally joined Yuan in opposing Xu's petition. "The court granted the motion over objections," the DA's statement read. No further legal remedies were announced in the aftermath of the ruling.
Yuan has made clear she considers this fight far from finished. Her decision to release the footage to the public was calculated, not impulsive — a move aimed at ensuring the case remains findable in ways the legal system no longer guarantees. In her court statement, she expressed fear that cadmium's long-lasting presence in the human body would continue to affect her health and her mother's for decades to come. The video she has now shared with the world ensures that millions of people have seen what she recorded inside that office — and what cost her and her family so much.
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