Engineer Caught on Camera Poisoning Female Coworker’s Water for Months

A California engineer who secretly poisoned a female coworker’s food and drinking water for more than a year was caught on a hidden camera, exposing a disturbing workplace crime that nearly cost the woman her life.

But despite initially facing a possible life sentence, David Xu ultimately received just two years of probation and credit for a single day in jail. Now, he’s seeking to have his felony conviction dismissed.

The case resurfaced after victim Rong Yuan, 50, released surveillance footage showing Xu tampering with her water bottle at Berkeley Engineering and Research, a California forensic engineering firm where they both worked.

According to a Berkeley Police Department investigation, Xu repeatedly contaminated Yuan’s food and water with cadmium, a highly toxic heavy metal, between 2017 and 2019.

For nearly two years, Yuan experienced mysterious and increasingly serious health problems, including severe vomiting, hair loss and repeated episodes that sent her to the emergency room.

Doctors initially struggled to determine what was making her sick. At one point, Yuan feared she had stomach cancer and even traveled to China seeking treatment.

Meanwhile, Xu appeared sympathetic to her suffering.

In November 2018, after Yuan emailed coworkers explaining that she was too sick to come to work, Xu encouraged her to stay home and suggested that mold inside their office might be responsible.

But Yuan eventually began suspecting something far more sinister.

After her mother noticed a strange taste in water taken from Yuan’s bottle, Yuan purchased a small surveillance camera and secretly installed it near her desk.

The footage changed everything.

In February 2019, the camera recorded Xu approaching her workstation and reaching toward the area where she kept her water. Another recording from March 4 showed him pouring a substance from a small container into her bottle.

Speaking publicly about the ordeal for the first time, Yuan told The San Francisco Standard that watching the footage left her terrified.

“My blood was frozen,” she recalled.

Investigators subsequently tested Yuan’s drinking water and discovered extraordinarily high concentrations of cadmium. One sample reportedly contained levels approximately 3.5 million times the federal drinking-water limit.

The contamination also extended beyond Yuan. Police found cadmium in blood samples from her parents, who had unknowingly consumed contaminated water while staying with her.

Xu was arrested in March 2019 and charged with premeditated attempted murder and two felony counts of poisoning.

Prosecutors initially pursued charges that could have resulted in a life sentence. Xu was later released on $2 million bail with electronic monitoring while the case proceeded through the courts.

However, the prosecution took a dramatic turn in September 2023 when Xu accepted a plea agreement under then-Alameda County District Attorney Pamela Price.

The attempted murder charge was dropped, and Xu pleaded no contest to a single felony count of poisoning. A no-contest plea results in a conviction without requiring the defendant to admit the underlying allegations.

At his March 2024 sentencing, Judge Kimberly Colwell reportedly described the agreement as extremely generous and increased Xu’s probation from the proposed one year to two years.

He also received credit for one day already spent in custody.

The financial outcome left Yuan equally frustrated.

Although she requested nearly $500,000 in restitution, a judge ordered Xu to pay $7,058. The decision followed a toxicology report submitted by his defense disputing whether cadmium exposure would cause lasting health problems.

Yuan strongly disagrees with that assessment and says she continues to experience medical complications that prevent her from working full time.

Now, another legal development has renewed her anger.

Xu completed probation in March 2026 and has petitioned Alameda County Superior Court to dismiss his felony conviction under California’s record-dismissal law.

His request is scheduled for a hearing Monday, October 12.

Under California law, qualifying defendants who successfully complete probation can generally obtain dismissal of their convictions. However, the process does not completely erase their criminal records, and certain government agencies can still access the information.

The Alameda County District Attorney’s Office is opposing Xu’s petition, according to court records reviewed by The San Francisco Standard.

Yuan plans to attend the hearing and exercise her right to address the court.

Her concerns extend beyond her own health. She worries that dismissing Xu’s conviction could make it easier for him to secure future employment without prospective employers learning the full history of the case.

Yuan has also published research describing the lasting health problems she believes her family suffered from cadmium exposure. Her father died in 2025 at age 78, although the available records do not establish that poisoning caused his death.

The case raises troubling questions about workplace safety, the long-term consequences of toxic exposure and how the criminal justice system handles serious poisoning cases.

For Yuan, releasing the surveillance footage is about ensuring that what happened to her is not forgotten.

Seven years after discovering the source of her mysterious illness, she is still fighting to have her experience heard as the man convicted in connection with her poisoning seeks another chance to clear his record.