Caught on Camera, Conviction Later Dismissed

Pipette dispensing liquid into test tubes in a laboratory rack — Photo: Sai Thaw Kyar / Shutterstock

Hidden-camera footage, lab toxicology, and a felony plea together tell a straightforward story: a Berkeley engineer repeatedly adulterated a colleague’s water with cadmium, was convicted of felony poisoning, completed probation, and later won dismissal of the conviction under California’s routine expungement statute—over prosecutors’ objection. The case is a study in how criminal proof, scientific attribution, and post-conviction relief operate on different tracks, often to unsettling effect for victims and the public.

At a Glance

Surveillance video documented a coworker entering the victim’s office and adding liquid to her water bottle on multiple dates.
Toxicology testing of the bottle identified cadmium at an extreme concentration; blood testing showed elevated cadmium in the victim and family members who drank from the bottle.
The defendant pleaded no contest to one felony poisoning count; attempted-murder and a second poisoning count were dismissed under the agreement.
After completing probation, he petitioned under Penal Code §1203.4 and the court dismissed the conviction despite the District Attorney’s opposition.

What the evidence established in the criminal case

According to Alameda County court filings and contemporaneous police reports, the victim, a Berkeley engineer, installed a small desk camera after months of unexplained illness. The recorded footage captured her coworker, David Xu, entering her office on separate occasions, unscrewing her water bottle, adding liquid, and replacing the cap. Police and prosecutors treated the videos as pivotal corroboration of opportunity and access, the linchpins in any non-accidental poisoning case built on circumstantial and forensic proof rather than eyewitness confession or a single catastrophic event. Reporters who reviewed the underlying descriptions in court records summarized the sequence as repeated, deliberate tampering that aligned with the victim’s symptom timeline.

Lab analysis of the bottle provided the toxicological anchor: outlets that reviewed the results reported cadmium at approximately 3.5 million times the federal drinking-water limit—a number so large it resolves disputes about trace contamination and forces the question from “Was there a hazardous substance?” to “How was it introduced, and how often?” Berkeley Police also documented a theory of repeated contamination of both food and water, consistent with a pattern rather than a single accidental exposure. When investigators turned to biological testing, they found elevated cadmium in the victim and two family members who had consumed water from the same bottle, a finding that connected environmental evidence to human exposure.

The legal path: charge, plea, and probation

Police arrested Xu in 2019 on premeditated attempted murder and two felony poisoning counts. Four years later, the case ended in a negotiated disposition: Xu entered a no-contest plea to one felony poisoning count in September 2023; the attempted-murder charge and a second poisoning count were dismissed. The plea structure is not unusual in complex felonies where prosecutors balance evidentiary risk, trial uncertainty, and the certainty of a felony conviction. Xu received probation rather than a prison term, a penalty that sparked public debate precisely because the evidence—video entry into the office, the metal’s concentration, and confirmed exposure—seemed so categorical.

Restitution, a separate component, diverged sharply from the victim’s request. Coverage describes a roughly $7,000 award against a claim approaching $500,000, underscoring how criminal restitution law hews to documented, compensable losses and court discretion rather than to broader, civil-style damages; the public often conflates the two, expecting a criminal sentence to resolve long-term medical and economic impacts in full, which it rarely does.

Expungement is procedural relief, not an acquittal

After completing probation, Xu petitioned for dismissal of his conviction under California Penal Code §1203.4. That statute withdraws a guilty or no-contest plea and enters a dismissal for eligible probationers; it is a longstanding, routine form of post-conviction relief that relaxes some collateral penalties, especially in private employment, without sealing the file or rewriting the historical fact that a conviction occurred. County and state guidance, as well as appellate decisions, are emphatic on this point: §1203.4 is designed to offer limited relief to those who successfully complete probation, not to relitigate guilt or innocence. In Xu’s case, reporting indicates the court granted the petition on October 12, 2026, over the District Attorney’s stated objection, which suggests the judge concluded statutory eligibility and the interests of justice were satisfied despite prosecutorial concerns.

The public-policy tension is real. A dismissal under §1203.4 means private employers may not see the conviction in routine background checks, even though law enforcement, licensing bodies, and courts can. Prosecutors argued against dismissal; the court exercised its discretion to grant it. Nothing in that procedural relief contradicts the original evidentiary record or the conviction that preceded it—it simply changes the defendant’s post-sentence legal posture, consistent with the statute’s design.

How toxicology, surveillance, and pattern evidence fit together

Intentional poisoning cases are solved at the intersection of three evidence streams. First, access and opportunity: who could physically reach the container, when, and under what pretext? Video of bottle tampering is rare but decisive. Second, environmental and biological testing: what was in the medium (water or food), at what concentration, and did exposed individuals show compatible biomarkers? Here cadmium, a heavy metal with well-characterized toxicodynamics, provided a measurable signature in both the bottle and in human samples. Third, repetition: isolated accidents are chaotic and singular; deliberate poisoning shows recurrence across dates, media (food and water), and locations. The Berkeley Police theory of multiple episodes fits that pattern, as did the timeline of the victim’s symptoms.

In the broader literature, most cadmium poisonings arise from occupational exposure rather than criminal acts. Diagnosis is inherently composite—clinical findings, blood and urine cadmium, imaging when kidneys or bones are affected, and environmental sampling often come together to confirm causation. That multifactorial approach explains why the Berkeley case, with both a demonstrable source and biomarker elevation, proceeded with unusual evidentiary clarity compared with many toxic exposures that remain probabilistic disputes.

Why the outcome feels dissonant—and what it teaches

The same features that made the case strong at charging—video corroboration, extreme toxicology, documented exposure—also make the post-conviction dismissal feel dissonant to lay readers. But those reactions stem from conflating systems. Criminal adjudication determined culpability through a no-contest felony plea, which is a conviction. Toxicology established exposure and mechanism. Post-conviction dismissal under §1203.4 addressed neither culpability nor science; it addressed the collateral legal status of a probationer who completed supervision. Each track did its work; they were never designed to answer the same question.

For victims, the practical stakes are significant. A dismissed conviction can narrow what prospective private employers learn about a former defendant, while leaving victims who continue to struggle with health or career losses feeling unrecognized by a system that moved on. For policymakers, the lesson is cleaner alignment: ensure that violent or deliberate poisoning offenses triggering substantial harm receive sentencing and post-conviction treatment that reflect their gravity, while preserving the rehabilitative channels §1203.4 was built to sustain for less consequential conduct.

In newly released footage, Berkeley chemical engineer David Xu is caught on a hidden camera putting a substance in his coworker’s water. She set up the camera after years of unexplained illness.

Prosecutors say he poisoned her with cadmium, a toxic heavy metal, for about 18… pic.twitter.com/IHpFRlmGnp

— California Courier (@cacourier) October 13, 2026

Bottom line

The Berkeley poisoning case is not ambiguous. Repeated bottle tampering was captured on video; cadmium in the water was measured at extreme levels; exposure was confirmed in blood; and the defendant resolved the case with a felony poisoning conviction before earning statutory dismissal after probation. The apparent contradiction between those facts and a “cleaner” record is not a contradiction at all—it is the predictable result of treating criminal guilt, scientific causation, and record relief as distinct questions governed by different laws. Understanding that separation is the only way to judge the outcome on its own terms—and to decide, as a matter of policy, whether those terms should change.