LOS ANGELES — A California scuba dive boat was operating in violation of Coast Guard regulations when crew members were sleeping and a pre-dawn fire killed 34 people, leaving grieving families wondering if a required night watchman could have saved their loved ones.

Thursday brought a disclosure from the National Transportation Safety Board that all six crew members were asleep aboard the Conception on Sept. 2 when the deadly blaze broke out.

The NTSB’s findings could aid federal authorities conducting a criminal investigation into the fire, who could bring charges under a statute known as seaman’s manslaughter. The law was enacted during the 19th century to punish negligent captains, engineers and pilots for deadly steamboat accidents that killed thousands.

Five crew members, including the captain, were asleep on the vessel’s second deck and survived. The sixth, a 26-year-old deckhand named Allie Kurtz, was sleeping below and perished with the boat’s 33 passengers.

The cause of the Sept. 2 blaze has yet to be determined. Crews raised the wreckage of the burned-out boat Thursday from waters off Santa Cruz Island where the vessel was anchored the night of the tragedy. The island is northwest of Los Angeles and about 20 miles from the mainland.

The Conception’s Certificate of Inspection, issued by the Coast Guard, requires a “roving patrol at all times” when passengers’ bunks are occupied.

The parents of Charles McIlvain, a 44-year-old visual effects designer who was onboard with his neighbor, said the missing roving watchman “disturbs us greatly.”

“Early detection may have made an incredible difference in outcome,” Clark and Kathleen McIlvain said in a statement.

Douglas Schwartz, an attorney for the Conception’s owner, Truth Aquatics Inc., said in a statement that a crew member was awake shortly before the fire, which started around 3 a.m. He said the crewman checked “on and around the galley area” around 2:30 a.m. The first mayday call from the captain was transmitted at 3:14 a.m.

He also touted the company’s safety record, noting it passed “every single annual Coast Guard inspection for the last 45 years, while hosting 450,000 divers on 1.3 million dives.”

Truth Aquatics Inc. filed a lawsuit last week in U.S. District Court under a pre-Civil War provision of maritime law aimed at limiting its liability.

The victims on the Conception were a diverse collection, including a girl celebrating her 17th birthday with her parents and a friend, a marine biologist who was leading the three-day scuba diving excursion, an Indian-born dentist and her husband from Connecticut, an environmental scientist and a professional photographer.

The last of the 34 bodies was pulled from the water Wednesday, and Santa Barbara County Sheriff Bill Brown released the names of the last seven to be identified during a news conference Thursday. It’s believed all died from smoke inhalation.

The NTSB report provided few additional details and noted that investigators have only interviewed three of the five surviving crew members, who said no mechanical or electrical issues had been reported before the fire.

The NTSB report did not mention potential charges, which would be part of the criminal probe.

An attorney who represented a Maine lobster boat captain charged in the deaths of two crew members who fell overboard when his boat flipped in high seas said he suspects prosecutors reviewing the information will ask if there was a watchman and, if not, what the captain had said or done.

“No watch? A boat that far offshore?” Michael Turndorf asked. “I think that fits the statute. I would be surprised if those are the real circumstances that somebody doesn’t get charged.”

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