LOS ANGELES — Federal investigators who examined the burned-out wreckage of a scuba diving boat have not been able to determine what ignited a fire that killed 34 people off the California coast, a law enforcement official said Friday.

Teams from the FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives left after spending two weeks reviewing what remains of the Conception, according to an official with knowledge of the investigation.

Parts of the vessel have been sent to labs for additional testing, said the official, who was not authorized to release the information publicly and spoke on the condition of anonymity. There is no indication anyone intentionally set the Sept. 2 fire.

Six crew members were asleep when the fire broke out before dawn and trapped those sleeping in bunks below deck. Coast Guard rules require a roving watchman, and authorities were looking into possible criminal charges that would likely focus on an obscure federal law known as the seaman's manslaughter statute.

The burned hull of the Conception is hoisted from the water off Santa Cruz Island, Calif., on Sept. 12, 2019. Brian van der Brug / Los Angeles Times via AP file

With the boat propped up by braces and scaffolding, investigators wearing protective suits walked over planks to inspect and document the burned vessel at Port Hueneme, a naval base more than 60 miles northwest of Los Angeles, the official said. Some parts of the boat washed away because it was submerged for two weeks off Santa Cruz Island.

Authorities also will examine hundreds of documents seized from the boat's owner, Truth Aquatics Inc., days after the fire.

The Coast Guard, FBI and U.S. attorney's office in Los Angeles are leading a criminal investigation into the blaze, and the National Transportation Safety Board is conducting a safety inquiry.

The captain and four crew members asleep on the vessel's upper deck survived the fire. The sixth, a 26-year-old deckhand named Allie Kurtz, was sleeping below deck and perished with the boat's 33 passengers.

Truth Aquatics preemptively filed a federal lawsuit under a pre-Civil War maritime law that shields boat owners from monetary damages in a disaster at sea.

Ryan Sims, a cook on the boat who broke his leg trying to escape the flames, claimed in a separate lawsuit that the boat was unseaworthy and operated in an unsafe manner.

Coast Guard records show the Conception passed its two most recent inspections with no safety violations.