Engineer Secretly Poisoned Female Co-Worker for Months, Then Blamed Her Mysterious Illness on Office Mold

A hidden camera captured the shocking moment that exposed a disturbing workplace poisoning case — and now, years after his conviction, the victim is fighting to ensure the man responsible cannot simply leave his criminal record behind.

For nearly two years, Rong Yuan endured a frightening medical mystery that left her struggling to work, repeatedly visiting hospitals and fearing that she might be suffering from a life-threatening disease. But the explanation for her worsening condition was far more disturbing than she could have imagined: investigators said her co-worker, David Xu, had repeatedly contaminated her food and drinking water with cadmium, a highly toxic heavy metal.

Yuan, then working at Berkeley Engineering and Research in California, began experiencing severe vomiting, dry heaving and hair loss in 2017. As her symptoms intensified, she sought medical help from numerous specialists and even travelled to China for treatment. Despite undergoing examinations, she struggled to find an answer to what was happening to her body.

Her family grew increasingly worried as her condition deteriorated. Her parents eventually travelled from China to stay with her, fearing that she might have a serious illness. Meanwhile, Xu appeared to show concern for his colleague, telling her to work from home when she was too sick to attend the office. He even suggested that mould in the workplace could be responsible for her symptoms — an explanation that would later take on a deeply disturbing significance.

The breakthrough came in January 2019, when Yuan’s mother noticed an unusual sour taste after drinking from her daughter’s water bottle. Yuan began to suspect that someone might be tampering with her food or drinks. Desperate to discover the truth, she purchased a small surveillance camera and secretly installed it near her desk.

What the camera captured would change everything.

Footage from March 4, 2019, showed Xu pouring a substance from a small white container into Yuan’s water bottle. Around 30 seconds later, he returned and moved the bottle, apparently mixing the substance inside. Yuan handed the recording to police that same day, providing investigators with crucial evidence in the case.

Laboratory testing revealed extraordinarily high levels of cadmium in the contaminated water. According to reporting by The San Francisco Standard, samples contained concentrations as high as 3.5 million times the federal drinking-water safety limit. Tests also detected cadmium in the blood of Yuan and both her parents, after her mother had unknowingly used water from the bottle to prepare family meals.

Xu was arrested in March 2019 and initially faced charges including premeditated attempted murder and felony poisoning. However, the case took a controversial turn in September 2023, when he entered a no-contest plea to one felony count of poisoning. The plea resulted in a conviction without an admission of the underlying allegations. The attempted-murder charge was dropped as part of the agreement.

In March 2024, a judge sentenced Xu to two years of probation, with credit for one day in jail. The judge described the deal as extremely generous given the circumstances. Yuan had sought nearly $500,000 in restitution but was awarded $7,058. She maintains that she continues to experience serious health problems and cannot work full time.

Now, the case has returned to the spotlight after surveillance footage emerged publicly and Xu sought to have his felony conviction dismissed under California law. He completed his probation in March 2026, but prosecutors have opposed his request. Although a dismissal would not erase the conviction from law-enforcement records, Yuan fears it could make the conviction less visible in certain employment background checks.

For Yuan, the legal battle is about more than a criminal record. It is about accountability after years of suffering, uncertainty and fear. She has spoken publicly about feeling failed by the justice system and is determined to have her experience taken seriously.

What began as an unexplained illness has become a disturbing case involving workplace trust, toxic poisoning and a long-running fight for justice. With the latest court proceedings bringing renewed attention to the evidence, Yuan’s story raises difficult questions about how the legal system responds when a victim survives an alleged attempt on her life but continues to suffer long after the criminal case has ended.

Source: The Sun