A California engineer who poisoned his female colleague with cadmium, a toxic heavy metal, is seeking to have his felony conviction dismissed seven years after his arrest.
David Xu secretly contaminated the food and drinking water of his co-worker, Rong Yuan, leaving her seriously ill and repeatedly hospitalised. He allegedly blamed her persistent vomiting on mould at their workplace.
Surveillance footage obtained by Yuan reportedly shows Xu pouring a substance from a small white container into her water bottle before returning about 30 seconds later to shake it.
Tests later found cadmium levels in her drinking water that were reportedly 3.5 million times above the federal safety limit.
Yuan, now 50, told the San Francisco Standard that the ordeal left her fearing for her life.
“My blood was frozen,” she said. “I almost died. I experienced death so, so close so many times. I cannot let him go.”
The ordeal began in 2017, shortly after Yuan joined Berkeley Engineering and Research, a forensic engineering firm in California.
Within weeks, she began experiencing hair loss, dry heaving and severe bouts of vomiting that repeatedly sent her to hospital. She underwent numerous medical examinations and travelled to China for treatment amid fears she could have stomach cancer.
As her condition deteriorated, her parents travelled from China to care for her.
In November 2018, Yuan emailed colleagues to explain that she was vomiting again and could not attend work. Xu replied that she should work from home until she felt better, before suggesting that the company’s premises might be affected by mould.
In January 2019, Yuan’s mother noticed an unusual sour taste after drinking from her daughter’s water bottle. Suspecting someone was tampering with her drinks, Yuan purchased a spy camera and installed it near her desk.
Footage recorded on February 11 showed Xu approaching her workstation and reaching towards the area where her bottle was kept, although the bottle itself was outside the camera’s view. A second recording, captured on March 4, allegedly showed him pouring a substance directly into it.
Yuan handed the footage to police that same day.
Berkeley Police Sergeant Jennifer Wilson described the evidence as shocking.
“No one would have believed her in the world that this was happening if she didn’t have proof of it,” Wilson said.
Subsequent tests found cadmium in the blood of Yuan and both her parents, after her mother unknowingly used contaminated water to prepare meals for the family.
Xu was arrested in March 2019 and initially charged with premeditated attempted murder and two felony poisoning offences.
However, prosecutors later offered him a plea deal that dropped the attempted murder charge. In September 2023, he pleaded no contest to one felony count of poisoning, a plea that carries the legal effect of a conviction without an admission of guilt.
At his sentencing in March 2024, Judge Kimberly Colwell described the deal as “extremely generous, considering everything in this case”.
She doubled his proposed probation period to two years and warned him against handling poison again.
“Please do not touch any poison at all. Ever. Ever,” she said.
Yuan had sought nearly US$500,000 in restitution but was awarded only US$7,058 after the court considered a defence toxicologist’s report disputing the long-term effects of cadmium poisoning.
She maintains that she continues to suffer debilitating health problems and is unable to work full-time.
Xu completed his probation in March 2026 and is now seeking to have his conviction dismissed under California law. Prosecutors have objected to the request.
Although the conviction would remain visible to law enforcement, Yuan fears it could be removed from background checks conducted by future employers.
“This legal system already failed me. This is my last resort,” she said.
