Evidence Preservation After a California Accident: What to Save and When

In California personal injury cases, the physical evidence that determines fault, documents injuries, and establishes the accident sequence is overwhelmingly collected — or lost — in the first three days after the accident. Understanding what to preserve, how to preserve it, and the legal consequences of evidence destruction is essential for anyone who believes they may have a personal injury claim.

The First Hour: Scene Evidence

Accident scene evidence begins deteriorating the moment emergency responders arrive. Vehicles are moved for traffic flow. Debris is cleared. Skid marks are washed by rain or traffic. Witnesses scatter. The first hour is the only opportunity to capture the scene as it was at the moment of impact.

If you are physically able, document the following before anything is moved: photographs of all vehicle positions relative to each other, lane markings, and fixed reference points (signs, curb cuts, crosswalks); close-up photographs of all points of contact damage on all vehicles; photographs of skid marks, gouge marks in the pavement, and debris fields; photographs of traffic signals, stop signs, yield signs, or other traffic controls in frame; photographs of road conditions (wet pavement, debris, potholes); and photographs of any visible injuries to yourself or other parties.

Collect contact information — name, phone number — from every witness present, not just the witnesses who approach you. Witnesses who appear bystander may leave before the police arrive and may not be identified in the police report.

Surveillance Footage: The 24–72 Hour Window

Traffic cameras, business security cameras, residential doorbell cameras, and parking lot cameras frequently capture accident scenes on video that is more reliable than any party's account. This footage is the most valuable evidence in many contested liability cases — and it is typically overwritten within 24 to 72 hours unless a preservation demand is received by the camera owner.

Identifying and demanding preservation of surveillance footage must happen the same day as the accident, or the following morning at the absolute latest. The preservation demand should go to: businesses near the accident scene whose cameras may have covered the roadway; the city or county transportation department for traffic monitoring cameras at the intersection; neighboring residences with visible doorbell or security cameras; and any nearby gas stations, banks, or parking facilities whose cameras cover the public roadway.

A written preservation demand — via email to the business owner or via certified mail for city traffic cameras — creates a legal record and may support a spoliation argument if the footage is overwritten after the demand. Without a preservation demand, a business has no legal obligation to retain footage beyond its normal retention period.

Vehicle Evidence and EDR Data

Modern vehicles contain an Event Data Recorder (EDR or "black box") that captures pre-crash speed, braking, throttle position, steering angle, seatbelt status, and airbag deployment trigger data for a few seconds before impact. This data is frequently dispositive in contested speed and braking disputes. The EDR is accessed through a specialized download tool; the download must be performed before the vehicle is repaired (because some repairs overwrite EDR data) or junked.

A vehicle that sustained significant damage after an accident may be declared a total loss and sent to a salvage yard within days. The EDR must be downloaded before this happens. A preservation demand to the insurance company — requesting that the vehicle not be destroyed before EDR download — should be sent immediately after any accident where speed or braking is in dispute.

Physical vehicle damage patterns — the shape, location, and depth of crush damage — also constitute evidence about the angle and relative speed of the collision. Before any vehicle is repaired, photographing the full damage profile from multiple angles and heights is essential.

Medical Documentation as Evidence

Medical records are the foundation of personal injury damages documentation. A medical evaluation on the day of the accident — or within 24 to 48 hours — creates a baseline medical record that connects the accident to the injuries. Delayed medical treatment gives the defense an argument that the injuries were not caused by the accident, or were not as serious as claimed.

Photograph injuries as they appear immediately after the accident and throughout the healing process. Bruising, lacerations, swelling, and abrasions often appear most dramatically in the days following an accident, not at the scene. A photographic progression documenting injury appearance from day 1 through full healing provides compelling evidence of the physical impact.

Retain all accident-related medical bills, pharmacy receipts, medical equipment receipts, home care bills, and transportation-to-treatment receipts. These are economic damages that require documentary proof.

Spoliation: Consequences of Evidence Loss

Spoliation is the intentional or negligent destruction or loss of evidence known to be relevant to litigation. In California, evidence spoliation can result in: an adverse inference jury instruction (the jury is told they may infer the destroyed evidence was unfavorable to the spoliating party); exclusion of evidence or claims; terminating sanctions in extreme cases; and independent tort liability for third-party spoliation. Evidence Code section 413 permits the jury to consider that a party who destroyed relevant evidence did so because it was adverse to them.

The most significant spoliation risk for personal injury claimants is the at-fault party or their insurer destroying or losing vehicle evidence. Sending a preservation demand to the insurance company covering the at-fault vehicle, and to any business whose premises may hold surveillance footage, creates the record necessary to pursue spoliation remedies if evidence is subsequently lost.