The fire that killed 34 people aboard the Conception dive boat on Labor Day four years ago near Santa Cruz Island started in a plastic trash can on the main deck, according to a report by the Los Angeles Times.

The Times said it reviewed a 197-page confidential report prepared by investigators with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, who arrived at a conclusion somewhat at odds with the previous working theory that the fire likely was sparked by lithium-ion batteries.

The report was written after ATF investigators built a full-scale mock-up of the Conception’s middle deck, and conducted a series of burn tests, the Times reported.

The deadly fire ignited in the pre-dawn hours on Sept. 2, 2019, as the Conception was anchored at Platt’s Harbor, on the island’s east side, at the end of a three-day holiday weekend scuba diving excursion.

The flames quickly engulfed the 75-foot, wooden-hulled vessel, trapping the 33 passengers and one crew member who were sleeping in the bunk room on the bottom deck.

Five crew members who were asleep on the top deck — including Capt. Jerry Boylan — escaped the burning boat and survived.

The Santa Barbara County sheriff’s Coroner’s Bureau determined that all the victims died of smoke inhalation.

A parallel investigation into the cause of the fire by the National Transportation Safety Board focused on charging areas where divers plugged in lithium-ion batteries that are used to power cameras, lights, computers and cell phones. Such batteries are sometime prone to catching fire.

However, the NTSB was unable to determine what sparked the blaze, saying it most likely was caused by “the electrical distribution system of the vessel, unattended batteries being charged, improperly discarded smoking materials, or another undetermined ignition source.”

The NTSB also reported in 2020 that there were polyethylene trash cans made by Rubbermaid throughout the Conception that were “highly combustible.”

The ATF said it found no evidence to support that the fire started where a tangled web of lithium batteries had been charging, although it noted that such batteries can ignite when they malfunction, the Times reported.

According to the Times, the report authored by ATF Special Agent Derek J. Hill in January 2021 concluded that “after conducting a systematic fire scene examination, reviewing witness statements, examining pre-fire and fire photographs and videos, and conducting test fires, by inspecting physical evidence, interpreting fire patterns, considering fire dynamics,” agents determined “the fire originated in the garbage container located under the staircase.”

While the ATF report zeroed in on a 23-gallon Rubbermaid Slim Jim trash bin that had been placed beneath the stairs of the main deck as the fire’s point of origin, it does not indicate what sparked the flames, the Times reported.

The report states that the cause remains “undetermined as investigators cannot rule out discarded smoking material, the open flame ignition of combustible materials such as paper towels located with the garbage container or an event unknown to investigators.”

ATF officials cited crew member Mickey Kohls telling NTSB and U.S. Coast Guard investigators he emptied four smaller trash bins into the 23-gallon receptacle about 2:35 a.m. the night of the fire, according to the Times report.

He was awakened about 3:12 a.m. by a popping sound and saw a glow from the middle deck.

Boylan, 69, of Santa Barbara, who has been accused of multiple failures in the deadly fire, has pleaded not guilty to a federal charge of misconduct or neglect of a ship officer.

The one-count indictment alleges that he “acted with a wanton or reckless disregard for human life by engaging in misconduct, gross negligence, and inattention to his duties on such vessel.”

The charge contained in the indictment alleges that Boylan — who “was responsible for the safety and security of the vessel, its crew, and its passengers” — failed his responsibilities in several ways, including by:

» Failing to have a night watch or roving patrol

» Failing to conduct sufficient fire drills and crew training

» Failing to provide firefighting instructions or directions to crewmembers after the fire started

» Failing to use firefighting equipment, including a fire ax and fire extinguisher that were next to him in the wheelhouse, to fight the fire or attempt to rescue trapped passengers

»Failing to “to perform any lifesaving or firefighting activities whatsoever at the time of the fire, even though he was uninjured”

» Failing to use the boat’s public address system to warn passengers and crewmembers about the fire

» Becoming the first crew member to abandon ship “even though 33 passengers and one crewmember were still alive and trapped below deck in the vessel’s bunkroom and in need of assistance to escape”

» Ordering other crew members to abandon the ship instead of instructing them to fight the fire or engage in other lifesaving activities

Boylan has denied any wrongdoing, and is scheduled to go to trial next month in federal court.

Numerous civil lawsuits also have been filed by family members of those who perished in the fire. They are at various stages in the legal process.