Berkeley Engineer Caught on Camera Poisoning Co-Worker Has Conviction Dismissed

A Berkeley engineer who was caught on hidden camera poisoning his co-worker’s drinking water with a toxic heavy metal has had his felony conviction dismissed, seven years after the disturbing workplace crime came to light.

David Xu, a former engineer at Berkeley Engineering and Research in California, was convicted of felony poisoning after his co-worker, metallurgist Rong Yuan, secretly recorded him tampering with her water bottle. Police said the substance was cadmium, a toxic heavy metal that can cause serious health problems.

Yuan had spent months experiencing unexplained symptoms including nausea, vomiting and hair loss. After becoming suspicious that someone was tampering with her food and water, she installed a hidden camera at her workplace. The footage showed Xu approaching her desk, pouring a substance into her water bottle and leaving. Testing later found cadmium in the water at extraordinarily high levels.

Xu was arrested in 2019 and initially faced charges including premeditated attempted murder and felony poisoning. He ultimately pleaded no contest to one felony poisoning charge under a negotiated agreement. In 2024, he was sentenced to probation rather than additional jail time.

The case has returned to public attention after Yuan released the hidden-camera footage and spoke publicly about what happened. She has said that she continues to deal with health problems and believes the poisoning also affected her parents after contaminated water was brought home from work.

On October 12, 2026, an Alameda County Superior Court judge granted Xu’s petition to dismiss the felony conviction after he completed his probation. Prosecutors and Yuan opposed the request, but the court granted it under California law.

For Yuan, the decision has reopened painful questions about accountability. She told the Los Angeles Times that “the system failed me,” arguing that the dismissal could make it harder for future employers to discover Xu’s conviction through standard background checks.

The case is a disturbing reminder that workplace danger is not always obvious. In this instance, the evidence that eventually exposed the poisoning came from a hidden camera installed by the person who had spent years trying to understand why she was becoming sick.

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