Proving Causation Without an Eyewitness: A 2026 California Court of Appeal Ruling

On August 4, 2020, 69-year-old Valencia took her daughter’s dog to Skyline Pet Hospital in San Mateo County for grooming. As she prepared to bathe the dog, it escaped through a propped-open door. Valencia followed it into the hallway. Moments later, she was found face-down and unresponsive. No one had seen her fall. She suffered serious head and neck injuries and died three days later.[1]

Her husband and son sued the hospital owner and building owner for negligence and premises liability. The grooming room floor was about 1.25 inches lower than the hallway, leaving an unmarked change in elevation at the doorway. There was no gate to stop animals escaping; one was installed afterward.

The defendants argued that, without an eyewitness, the family could not establish what caused the fall. The trial court agreed, excluded parts of the plaintiffs’ expert testimony and granted summary judgment. The Court of Appeal reversed.[2]

The legal question was as to whether a plaintiff could prove causation when nobody actually saw the accident. California’s appellate court said a case can proceed when physical evidence, expert analysis and reasonable inferences together create a genuine factual dispute. An unwitnessed fall does not automatically make the explanation speculative.[3]

The trial court had placed too much weight on testimony that Valencia was seen leaving the grooming room, but not tripping at its threshold. As the appellate court explained, someone who falls down stairs and cannot recall what happened may still have evidence of why they fell. Direct observation is not the only route to proof.

How the Plaintiffs Built the Case Without a Witness

The family relied on two biomechanical engineers who identified the threshold as a likely cause of the trip. A veterinarian also addressed the unsecured dog, the open door and the safety procedures the facility allegedly failed to follow.[4]

That combination mattered. The experts did more than identify a possible hazard. They connected the room’s layout and the dog’s escape to a plausible sequence of events. They also considered alternative explanations, helping narrow the possible causes.

The appellate court found that the trial judge had dismissed portions of this work as speculative without adequately examining the experts’ underlying information and methods. That was a critical error.[5]

The Substantial Factor Standard

California law does not require negligence to be the only possible cause of an injury. The relevant question is whether it was a substantial factor in bringing about the harm.[6]

That distinction is particularly important when nobody can reconstruct every second of an accident. The family did not have to establish the precise movement of Valencia’s feet. They needed enough reliable evidence for a reasonable jury to find that the defendants’ conduct substantially contributed to her fall.

The appellate court concluded that they had met the threshold for a trial. This is not that causation had already been proved.[7]

What This Ruling Means for PI Practice is to:

• Choose experts for their reasoning, not just their conclusions. In Osaze, the engineers and veterinarian addressed different pieces of the same event. Their value lay in explaining how the evidence supported the proposed cause, rather than merely endorsing the family’s position.[8]
• Document the scene before it changes. A small height difference, an open doorway or a missing gate may seem ordinary until an injury occurs. Measurements, photographs and contemporaneous records can become essential. Repairs may happen quickly, making early preservation all the more important.
• Consider alternative causes from the start. A defense attorney may point to distraction, illness or another obstacle. A persuasive causation analysis should engage with plausible alternatives rather than ignore them.
• Prepare for summary judgment early. Waiting until trial to assemble a coherent explanation is risky. Expert methods, medical evidence and physical facts should fit together long before a dispositive motion arrives.

The Ruling

The Court of Appeal reversed the judgment and returned the case to the trial court. It held that the plaintiffs had produced enough evidence to raise a triable causation issue. [9]

The lesson for PI firms is straightforward, which is no eyewitness does not mean no case. But an inference must be built, not assumed. In Osaze, careful attention to the scene, the experts’ methods and competing explanations gave the family an opportunity to have a jury hear its claim. [10]

[1] Osaze v. Gee, No. A173403, slip op. at 2–7 (Cal. Ct. App. Sept. 29, 2026) https://law.justia.com/cases/california/court-of-appeal/2026/a173403.html

[2] Id. at 7–8

[3] Kaney v. Custance, 74 Cal. App. 5th 201, 217–20 (2022) https://law.justia.com/cases/california/court-of-appeal/2022/b302835a.html.

[4] Osaze, No. A173403, slip op. at 7–16

[5] Sargon Enters., Inc. v. Univ. of S. Cal., 55 Cal. 4th 747, 771–72 (2012) https://law.justia.com/cases/california/supreme-court/2012/s191550.html.

[6] Osaze, No. A173403, slip op. at 17–18

[7] Kaney, 74 Cal. App. 5th at 217–20

[8] Osaze, No. A173403, slip op. at 23–30

[9]  Id. at 33

[10] Id. at 30–33