SANTA BARBARA, Calif. — What caused the Conception to catch fire, killing 34 people?

Investigators are not sure, but they hope the burned remains of the vessel can provide the answer.

The Conception has now been towed to shore and is expected to be taken to a naval facility, where a team of investigators from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives will examine its power, fuel and electrical systems, federal officials said.

Workers on Thursday raised the remains of the Conception from the seafloor of Platts Harbor after a weeklong delay because of strong winds. A massive crane with yellow straps slowly lifted the vessel up the side of a barge. Much of the boat had been gutted, with only the hull and the lower berths remaining intact.

“This is the most critical stage,” said Coast Guard Petty Officer 1st Class Mark Barney. He noted the importance of keeping what’s left of the boat intact for investigative purposes.

More than a week after the deadliest maritime fire in modern California history, investigators are still trying to determine what sparked the blaze and what caused the fire to quickly consume the vessel.

There have been several theories. The designer of the dive boat told the Los Angeles Times that he believed the fire began in the sleeping quarters with a lithium battery charger. A crew member told a good Samaritan aboard a nearby vessel immediately after the fire that the blaze may have erupted at a charging station used by passengers in the galley.

Investigators from the FBI, the ATF and the Coast Guard had launched a criminal investigation by the weekend, searching the Santa Barbara Harbor office of the Conception’s operator, Truth Aquatics, on Monday, and inspecting two of the firm’s other charter boats.

The National Transportation Safety Board said Thursday that when fire ignited aboard the Conception in the predawn dark, none of the crew members were awake to alert the passengers sleeping below deck, even though federal law required that the charter boat have a night watchman.

The crew members were sleeping in a berth behind the wheelhouse. By the time they woke and jumped down to the main deck, they found the galley and salon engulfed in flames. The horror was plain: The main bunk room where their 33 customers and a fellow crew member dozed lay directly below, in the belly of the boat.

The only way out was through the inferno. No one made that escape.