Berkeley engineer is caught on camera poisoning female colleague’s drink before blaming her illnesses on mold in their office

Published: 04:22 EDT, 13 October 2026 | Updated: 04:22 EDT, 13 October 2026

A California engineer was caught poisoning his female colleague’s water bottle with a highly toxic metal after she spent nearly two years suffering from a mysterious illnesses.

David Xu, a metallurgist at Berkeley Engineering And Research, had previously suggested that mold in their office could be making her sick.

But Xu had actually been secretly contaminating coworker Rong Yuan’s food and drinking water with cadmium, a poisonous heavy metal capable of causing severe organ damage and even death.

Evil colleague: Hidden-camera footage shows Berkeley engineer David Xu at the desk of his colleague Rong Yuan, whose food and water he poisoned with toxic cadmium for over a year

The horrifying campaign unfolded between 2017 and 2019, leaving Yuan repeatedly hospitalized, vomiting uncontrollably, and fearing she was dying from an undiagnosed illness.

In a disturbing twist, Xu appeared to play the concerned colleague, even encouraging Yuan to stay home when she became too sick to work.

When she emailed colleagues on November 27, 2018, explaining that she was vomiting again, Xu responded: ‘You should work from home until you feel better. No reason to rush in.’

He then offered a seemingly innocent explanation for her deteriorating health: ‘I think BEAR is moldy.’

Now, seven years after Xu’s arrest, Yuan has released surveillance footage taken on hidden cameras showing how she caught the man in the act.

The videos, obtained by the San Francisco Standard, were recorded using a hidden camera Yuan purchased from Amazon after becoming convinced somebody was deliberately poisoning her.

One recording, dated February 11, 2019, shows Xu approaching her desk and reaching toward the area where her water bottle was positioned.

Another, captured on March 4, shows him pouring a substance from a small white container into her bottle before returning approximately 30 seconds later to rotate it.

Discussing the first time she watched the footage, Yuan told the Standard: ‘My blood was frozen. I almost died. I experienced death so, so close so many times. I cannot let him go.’

The revelations have emerged as Xu, 41, prepares to ask an Alameda County judge on Monday to dismiss his felony conviction after completing a remarkably lenient sentence.

Lenient sentence: Xu pleaded no contest to poisoning Yuan after initially facing attempted murder charges. He received two years of probation and credit for a day behind bars

Despite initially facing charges that could have resulted in life imprisonment, Xu received just two years of probation and credit for a single day behind bars.

Yuan, who says she continues to suffer debilitating health problems, is furious that the man responsible could now be dismissed.

She said: ‘This legal system already failed me. 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.

She remembered telling her co-worker: ‘I know how to use all these tools, I’ve even repaired them.’

Determined to avoid confrontation, she decided to keep her distance.

Yuan recalled thinking at the time: ‘I’ll just simply do my work, and he can do whatever he wants.’

Chilling act: Xu is seen leaning over his colleague’s desk and pouring a substance from a small white container into her water bottle in surveillance footage recorded on March 4, 2019

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.

Yuan recalled: ‘I began to feel like I was dying.’

Further terrifying episodes followed, prompting repeated hospital visits, consultations with specialists and even a trip to China to seek medical treatment.

Yuan feared she had stomach cancer, but the medical examinations failed to explain her symptoms.

Her worried parents eventually traveled from China to help care for her.

No choice: Yuan installed a hidden camera near her desk at work after suffering for months with a mysterious illnesses

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 ultimately exposed 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.

Wilson said: ‘It was shocking. 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 released on $2million 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.

The judge warned: ‘Please do not touch any poison at all. Ever. Ever.’

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.

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 he did to her.

Yuan says her health remains damaged and she is unable to work full time.