The public story is that the Eaton Fire cause took eighteen months. The documents tell a more specific story: the origin was found in a week, the electrical conclusion was written and signed in four months, and then almost everything after that was spent getting hands on the hardware and putting it under instruments.
The nine days
Field work ran from January 8 to January 16, 2025. In that window the team located the general origin area, flagged the fire pattern indicators, interviewed a long list of residents, collected the security video, recovered beaded metallic material from Tower #3, swept the ground with magnets and metal detectors, flew LiDAR and drone missions, obtained surveillance footage from a United States Marine Corps facility through a Department of Defense clearance request, and pulled the 911 recordings. On January 16 the scene was released and security was stood down.
The investigation continued past that, but the intensity drops. February 20 brought the substation tours and the La Canada Flintridge tower visit. March 19 moved the evidence into LACoFD storage. April 9 was a surveillance flight looking for arcing along the conductors above Eaton Canyon Falls.
The signature that sat for fourteen months
The single most striking fact in the release is a date on a signature line. The initial Eaton Fire Investigation Report is signed by Captain Rick Yartz on 5/22/25.
That report already states the conclusion: the cause of this fire is electrical in nature, caused by an electrical event that occurred at approximately 1811 hours within a grouping of three SCE transmission towers. It was released to the public on August 4, 2026, fourteen and a half months later.
The report also explains why it was not the end of the matter. Its own closing pages read as a list of things still outstanding. The Investigation Team electrical engineers are waiting to view physical evidence of SCE infrastructure and are still waiting to receive the SCE data that was requested on January 20, 2025, and the Investigation Team has not received any of the requested data currently. The Eagle Rock to Gould fault detected at 1811 hours is described as an item of interest still being investigated. And the last line before the signature: supplemental reports will be added to the investigation narrative as new information is discovered.
That is an investigator saying, in May 2025, that he knows what happened and cannot yet prove which piece of metal did it.
Who had the evidence
The supplemental report opens the second phase with a sentence that explains the whole delay. The SCE electrical utility equipment was not available for examination, analysis, or testing at the time of the initial investigation, and required extensive planning and resources from SCE to remove and store it.
This is a real physical constraint, not only a procedural one. The evidence is transmission tower hardware standing on a spur ridge that cannot be reached by vehicle, in a canyon that had just burned. Taking it down intact, preserving it, and giving every party equal access is a substantial operation. The initial report notes that Eaton Fire SCE Field Equipment Protocols were negotiated, intended to provide all investigative parties equal access and ability to inspect, test and preserve the towers and the equipment directly attached to them, and that the evidence removal process started on April 21, 2025 and was ongoing at the time of writing. The removed equipment was preserved and stored at a facility in Azusa.
Alongside that sits the unfulfilled data. Requests went to SCE on January 20 and January 31, 2025, and had not been answered by late May. We state that as the document states it, without inferring a reason.
The laboratory sequence
The supplemental report is where the eighteen months become legible. It is short, four pages, and most of it is a chain of custody.
Expert retention. Early in the investigation CAL FIRE retained an electrical engineer to assist with possible electrical sources of ignition associated with SCE owned transmission lines in the general area of the origin. During the warehouse exams CAL FIRE also retained a metallurgist for the laboratory and warehouse examinations and testing of the utility equipment. Both names are redacted.
Warehouse examinations, from late July 2025. Following SCE's disassembly, removal and storage of the equipment, examinations began at the warehouse storage facility in late July 2025 and continued incrementally for several months at the warehouse in Azusa. During these examinations specific items of evidence were identified and prepared to be examined in a laboratory setting.
Laboratory testing, latter part of 2025. Testing occurred at a laboratory in El Segundo.
Kentucky, December 9 to 12, 2025. Certain pieces of evidence could not be viewed or examined due to size constraints on the equipment at the El Segundo laboratory. The parties identified a laboratory in Bowling Green, Kentucky with a large chamber scanning electron microscope big enough to take the larger pieces. Chain of custody is documented across the transport: personnel opened and inventoried the container on arrival and handed it to a named lab operator, testing ran from December 9 to December 12, 2025, and afterward the evidence was inventoried, placed in a secure container, sealed, and transported back to the Azusa warehouse. The investigator writes that he personally supervised the evidence during its transport to and from the laboratory, ensuring the chain of custody was maintained throughout.
Metallography and X ray diffraction, July 2026. Metallography took place at an engineering laboratory in Signal Hill on July 22 and 23, 2026. X ray diffraction took place at a research facility in Goleta on July 24, 2026.
Final reports, July 22, 2026. CAL FIRE Assistant Chief Brian Hawkins provided the final versions of the experts' metallurgy, failure analysis and electrical investigation reports, filed as attachments 10.23 and 10.24. The supplemental report is signed the same day.
One other item is dated in this stretch. On June 30, 2026 the Los Angeles County Sheriff's Department provided the homicide death investigation files for all nineteen victims.
What the delay was, and what it was not
Read against the documents, the eighteen months resolve into three distinct periods. The first ten days were the fire investigation proper. The next six months were spent waiting for equipment to be removed from a mountain and made available on terms every party could accept. The final year was laboratory science on that hardware, ending with instrument work in the last week before the supplemental was signed.
Two weeks after the final expert reports landed, the county released everything. The gap between the determination and the publication was short. The gap between the fire and the determination was mostly the gap between an investigator's conclusion and the physical proof of which component failed, and that proof was in someone else's custody.