US engineer caught on camera tampering with colleague’s water bottle

A California chemical engineer, David Xu, who pleaded no contest to poisoning a colleague, was captured in hidden-camera footage appearing to show him tampering with her water bottle using cadmium, a toxic heavy metal.

Xu, a metallurgist at Berkeley Engineering and Research, was accused of poisoning his colleague, Rong Yuan, through her food and drinking water for nearly 18 months between 2017 and 2019, according to reports by The San Francisco Standard and the New York Post.

The footage, recorded by Yuan in 2019, reportedly showed Xu putting a substance into her water bottle. Subsequent laboratory tests detected cadmium in the bottle.

Speaking to The San Francisco Standard, Yuan described her reaction when she watched the footage for the first time.

“My blood was frozen,” she said, adding, “I almost died. I experienced death so, so close so many times. I cannot let him go.”

Yuan reportedly began experiencing serious health problems in 2017, including severe vomiting that sometimes required emergency hospital treatment.

In an email to colleagues on November 27, 2018, she reported feeling unwell and said she needed to take a sick day. Xu responded by advising her to work from home until she felt better.

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“I think BEAR is moldy,” he reportedly wrote, referring to the workplace.

The poisoning was uncovered in early 2019 after Yuan installed a hidden camera at her desk. The footage reportedly captured Xu tampering with her water bottle.

A laboratory report reviewed by The San Francisco Standard found cadmium in the bottle at levels up to 3.5 million times the federal limit for drinking water.

Yuan’s parents were also exposed after inadvertently consuming contaminated water. Her mother reportedly noticed a sour taste on one occasion and had used water from the bottle to prepare food.

Xu was arrested in March 2019 on charges of attempted murder and poisoning. In September 2023, he accepted a plea deal and pleaded no contest to a single felony count of poisoning. The attempted murder charges were dropped.

In March 2024, he was sentenced to two years of probation and received credit for one day spent in custody.

Yuan had sought nearly $500,000 in restitution for the harm suffered by her and her family. However, Xu was ordered to pay $7,058.

He completed his probation in March 2026 and is seeking to have his felony conviction dismissed under California’s expungement process. The process allows eligible defendants who have fulfilled their probation requirements to apply for dismissal of their convictions.

Yuan said she continued to suffer long-term health effects from the poisoning and was unable to work full-time.

She also published a research paper on the long-term health consequences suffered by her and her parents, dedicating it to her late father, who died of heart failure.

(punchng)