LOS ANGELES — Late on the eve of Labor Day 2019, as the crew of the Conception buttoned up the 75-foot dive boat, one of the galley hands plugged in his cellphone and saw sparks fly from the socket, just before he headed to bed.

He later told investigators that "while still in a sleep-like state, he had heard a pop and then a crackle downstairs," followed by another crew member yelling, "Fire! Fire!" — according to National Transportation Safety Board records released Wednesday.

The galley hand and four other crew members who had been jolted awake tried to make their way down from the wheelhouse atop the three-deck boat, but it was too late.

By then flames had engulfed the Conception's main deck, blocked stairways and trapped 33 divers and one crew member in the bunk room in the belly of the wood-hulled boat, killing all of them in one of California's worst maritime disasters.

The only survivors were the five crew members who managed to jump into the water near Santa Cruz Island. They included Capt. Jerry Boylan, who apparently quickly realized the gravity of the situation.

"The second galley hand recalled that when the captain came to the surface of the water, he said, 'Oh my God, all those people,'" the records state.

Autopsies later determined that all died of smoke inhalation.

The NTSB records, which include factual reports and transcripts of witness interviews, provide the fullest account yet of the Sept. 2, 2019, accident off the Ventura County coast, but they do not pinpoint a cause of the fire.

"No physical evidence was recovered that could be identified as an ignition source or indicate a specific ignition location within that area," the records noted. "Therefore, the cause of the fire is undetermined."

The most intense area of the blaze appeared to be in the salon, on the main level of the boat, where "numerous electronic devices" were being charged, the records noted. Lithium-ion batteries commonly used for computers, cameras and other devices had caused other maritime and aviation fires, it said.

"It is therefore reasonable to include lithium-ion battery failure as a possible ignition source in this fire scenario," the report stated. "Another potential source of ignition is the vessel's electrical system in the salon compartment."

Investigators noted that the fire could also have been caused by an undetermined ignition source, such as discarded smoking materials.

The NTSB reports also identified "potential fire safety issues," including lack of regulations requiring smoke detectors, flammability of interior materials, size and accessibility of emergency exits, and the fact that both exits from the bunk room led to the same compartment — which was engulfed in fire.

The newly released records underscored the findings of a preliminary investigation by the NTSB that previously determined that the five crew members were asleep in their berths on the top deck when the blaze broke out about 3 a.m., despite a requirement that the vessel have a roving watch at night.

Glen Fritzler, the owner of Truth Aquatics Inc., which operated the Conception, has denied wrongdoing and insisted that the boat's crew members were awake when the fire was detected. His attorney has said that a crew member was in the salon less than half an hour before the fire was discovered.

The NTSB interviewed captains and crew members from other Truth Aquatics vessels, and all stated that the practices on their vessels were the same as those on the Conception. No roving watches were set while in port or at anchor, according to the report. The Vision captain stated that he believed that having one of the crew members sleep in the bunk room "somehow fulfilled" the roving watch requirement.

Fritzler recently declined to comment but previously told the Los Angeles Times he suspects that lithium-ion batteries were a source of the fire. He said he was never warned about the potential dangers by the U.S. Coast Guard.

The disaster remains under investigation by the NTSB. It also is under criminal investigation by the U.S. Coast Guard and the FBI under the supervision of the U.S. attorney. The Bureau of Alcohol, Tobacco, Firearms and Explosives told the Times this month it was completing its report on the cause of the fire.

After the disaster, U.S. Coast Guard criminal investigators and the FBI served a search warrant on Truth Aquatics as part of what the Coast Guard spokesman called a "potential seaman's manslaughter" investigation that carries up to 10 years in prison.

In July, Boylan met with federal prosecutors supervising the investigation in Los Angeles. They presented the captain with evidence from the investigation — a move usually done when "there is sufficient evidence to bring criminal charges," according to a recent civil filing by attorneys for the owners of Truth Aquatics.

Jeff Goodman, an attorney for nine of 34 families who lost loved ones in the fire, said he will review the voluminous NTSB records released Wednesday on what he called a "preventable tragedy."

"We will hold those responsible for this disaster fully responsible," he said. "It is premature to reach conclusions. We are going to be analyzing it in the days ahead with legal and technical experts."

Goodman's law firm has filed a lawsuit in U.S. District Court in Los Angeles, alleging that the boat's owners and crew were negligent in their training and operations of the vessel, including failing to have the required roving night watch.

The NTSB has announced it will hold a public hearing Oct. 20 to announce its findings and recommendations.

Built in 1981 in Long Beach, the Conception was one of three dive boats operated out of Santa Barbara Harbor by Fritzler, who began diving as a 12-year-old and has been with the company since 1979.

The boat's three-level design was similar to other dive vessels: sleeping quarters below deck, a main deck that includes a covered galley toward the bow with open-air dive area at the stern, and the wheelhouse with the captain's controls at the top.

It featured double- and triple-stacked bunks, with a passenger limit of 46 — the count was 13 below that capacity when the fire occurred. Some divers have dubbed the popular configuration a "cattle boat" style of excursion, because of the tight space and lack of staterooms and other cabin amenities.