A California engineer was recorded secretly adding a highly poisonous metal to a female colleague’s water bottle after she endured almost two years of unexplained, debilitating illness.
David Xu, a metallurgist at Berkeley Engineering and Research, even floated the possibility that mold inside their workplace was responsible for her worsening condition.
Behind the scenes, however, Xu was accused of contaminating Rong Yuan’s food and drinking water with cadmium, a toxic heavy metal that can cause serious organ damage and prove fatal.
The alleged poisoning took place from 2017 through 2019. During that period, Yuan was hospitalized several times, suffered violent bouts of vomiting and became convinced that an unknown disease might kill her.
Xu appeared to act as a sympathetic coworker, at one point advising Yuan to remain at home when she was too ill to report to the office.
After Yuan emailed colleagues on November 27, 2018, to say she was vomiting again, Xu replied: “You should work from home until you feel better. No reason to rush in.”
He also offered what appeared to be an explanation for her illness, writing: “I think BEAR is moldy.”
Seven years after Xu’s arrest, Yuan has made public surveillance footage that she says helped expose the person behind her prolonged suffering.
Hidden-camera footage appears to show Berkeley engineer David Xu at coworker Rong Yuan’s desk, where prosecutors said he poisoned her food and water with cadmium for more than a year
David Xu, 41, pleaded no contest to poisoning fellow engineer Rong Yuan after initially being charged with attempted murder. He received two years of probation and credit for one day served in custody
The recordings, obtained by the San Francisco Standard, came from a concealed camera Yuan bought on Amazon after concluding that someone might be intentionally poisoning her.
In footage dated February 11, 2019, Xu can be seen walking toward Yuan’s desk and reaching into the area beside her water bottle.
A second video, recorded on March 4, appears to show Xu emptying material from a small white container into the bottle. Roughly 30 seconds later, he returns and turns the bottle.
“My blood was frozen,” Yuan, now 50, told the Standard after viewing the recordings for the first time.
“I almost died. I experienced death so, so close so many times. I cannot let him go.”
The footage has surfaced as Xu, 41, prepares to ask an Alameda County judge on Monday to set aside his felony conviction after completing a sentence widely criticized as unusually lenient.
Although the original charges carried the possibility of a life sentence, Xu ultimately served no additional jail time beyond credit for one day and was placed on probation for two years.
Yuan says she still deals with severe health problems and is outraged that Xu may now have his conviction dismissed.
Surveillance footage from March 4, 2019, appears to show Xu leaning over his colleague’s desk and pouring a substance from a small white container into her water bottle
After months of unexplained illness, Yuan installed a hidden camera and captured footage of Xu allegedly tampering with her drinking water, evidence that eventually led to his arrest
‘This legal system already failed me,’ she said. ‘This is my last resort.’
The nightmare began shortly after Yuan joined Berkeley Engineering and Research, a forensic engineering company, in January 2017.
Both scientists had earned doctorates through the University of California, Berkeley, and specialized in studying metals.
Yuan recalled an uncomfortable first encounter when Xu told her she could not use the company’s materials characterization laboratory.
‘I know how to use all these tools,’ she remembered telling him. ‘I’ve even repaired them.’
Determined to avoid confrontation, she decided to keep her distance.
‘I’ll just simply do my work, and he can do whatever he wants,’ she recalled thinking.
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Within weeks, however, she began experiencing alarming symptoms, including hair loss and dry heaving.
By July 2017, her condition had deteriorated dramatically.
After drinking from her water bottle one morning, she became desperately ill and a neighbor rushed her to the emergency room.
‘I began to feel like I was dying,’ she recalled.
Further terrifying episodes followed, prompting repeated hospital visits, consultations with specialists and even a trip to China seeking medical treatment.
Yuan feared she had stomach cancer, but the medical examinations failed to explain her symptoms.
Berkeley Engineering and Research, where Xu and Yuan worked as metallurgists. Yuan endured repeated hospital visits, severe vomiting and hair loss before discovering that her water had been deliberately contaminated
Her worried parents eventually traveled from China to help care for her.
The breakthrough came in January 2019 when her mother noticed a peculiar sour taste after drinking from Yuan’s water bottle.
Suspecting someone was tampering with her drinks, Yuan installed the hidden camera that would ultimately expose Xu.
Police subsequently discovered massive concentrations of cadmium in her water.
Laboratory testing revealed levels reaching 3.5 million times the federal drinking-water limit, according to a report reviewed by The Standard.
Blood samples from Yuan and both her parents also tested positive for cadmium. Her mother had unknowingly used contaminated water from the bottle to prepare family meals.
Berkeley Police Sergeant Jennifer Wilson, who investigated the case, described her astonishment upon reviewing the surveillance footage.
‘It was shocking,’ Wilson said. ‘No one would have believed her in the world that this was happening if she didn’t have proof of it. … It really launched this case immediately.’
Xu was charged in March 2019 with premeditated attempted murder and two felony poisoning offenses.
He was subsequently released on $2 million bail with GPS monitoring, while restrictions on his movements were progressively relaxed.
In September 2023, prosecutors under then-Alameda County District Attorney Pamela Price offered Xu a plea agreement that dropped the attempted murder charge.
He pleaded no contest to one felony count of poisoning, a plea that carries the legal effect of a conviction without admitting the underlying allegations.
The proposed punishment was one year of probation.
At his March 2024 sentencing, Judge Kimberly Colwell described the arrangement as ‘extremely generous, considering everything in this case’ and increased probation to two years.
She also ordered Xu to stay away from Yuan and her parents.
‘Please do not touch any poison at all. Ever. Ever,’ the judge warned.
Yuan had sought almost $500,000 in restitution but was awarded just $7,058 after the court considered a defense toxicologist’s report disputing that cadmium poisoning would produce long-term health effects. She strongly contests those conclusions.
Xu completed probation in March 2026 and is now seeking relief under California’s record-dismissal law.
Although a successful petition would not erase his conviction from law-enforcement records, Yuan fears it could prevent future employers from discovering what happened.
Yuan says her health remains damaged and she cannot work full time.
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