A California engineer was secretly filmed contaminating a female colleague’s water bottle with a deadly heavy metal after she spent almost two years battling unexplained illness.
David Xu, a metallurgist at Berkeley Engineering and Research, even floated the possibility that mold inside their workplace was responsible for Rong Yuan’s worsening health.
Instead, investigators determined that Xu had been secretly adding cadmium to Yuan’s food and drinking water. The highly toxic metal can cause serious organ damage and may be fatal.
The alleged poisoning took place from 2017 through 2019. During that period, Yuan was hospitalized several times, endured violent bouts of vomiting and feared she might die before doctors could identify the cause.
Xu appeared to present himself as a sympathetic coworker, at one point advising Yuan to remain at home when she was too ill to report to work.
After Yuan emailed colleagues on November 27, 2018, to say she had begun vomiting again, Xu replied: “You should work from home until you feel better. No reason to rush in.”
He also suggested a possible explanation for her mysterious symptoms, writing: “I think BEAR is moldy.”
Seven years after Xu’s arrest, Yuan has made public surveillance footage that shows how she eventually uncovered the person she believes was responsible for poisoning her.
Hidden-camera video appears to show Berkeley engineer David Xu at the desk of coworker Rong Yuan, whose food and water were contaminated with toxic 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 was sentenced to two years of probation and received credit for one day in custody
Yuan bought a concealed camera from Amazon after becoming convinced that someone was deliberately making her sick. The recordings were obtained by the San Francisco Standard.
In footage recorded on February 11, 2019, Xu can be seen walking to Yuan’s workstation and reaching toward the area where she kept her water bottle.
A second video, dated March 4, shows him emptying material from a small white container into the bottle. About 30 seconds later, he returns and turns the bottle.
“My blood was frozen,” Yuan, now 50, told the Standard after watching 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 erase his felony conviction after completing what Yuan considers an exceptionally light sentence.
Xu originally faced charges carrying the possibility of life in prison. He ultimately received two years of probation and credit for just one day spent behind bars.
Yuan says she still suffers serious, debilitating health problems. She is now enraged that Xu could have his conviction dismissed after being held responsible for the poisoning.
Surveillance footage recorded on 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 that captured footage of Xu allegedly tampering with her drinking water and helped lead 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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