LOS ANGELES — Coast Guard officials have recovered the bodies of 33 people who died in a massive fire aboard the Conception that started as the 75-foot vessel was anchored off the coast of Santa Cruz Island on Labor Day. One person is still missing, authorities said Wednesday.

Thirty-nine people were on board for a three-day scuba diving trip when the fire broke out. Five crew members jumped overboard and paddled to a nearby vessel. They survived. The passengers and a sixth crew member were asleep below deck and were likely trapped by the flames, officials said.

Officials had recovered the remains of 20 people — 11 female and 9 male — as of Tuesday. Thirteen more bodies were found as of Wednesday, Coast Guard Lt. Cmdr. Matt Kroll said.

The names of those who perished in the fire off the Ventura County coast have not been released by officials.

On Wednesday morning, about a dozen divers with the FBI gathered at Santa Barbara Harbor to search for the last victim. They will join divers from other government agencies to comb the area where the Conception sank days earlier, said Santa Barbara County sheriff’s Lt. Brian Olmstead.

About three dozen divers have participated in search efforts over the last few days. They go out for hours at a time and return “emotionally drained,” Olmstead said.

“Our priority is trying to find the last victim and also items that would be of interest to find out what happened,” he said. “You want to bring closure to the families.”

The Conception is submerged in 60 to 65 feet of water. Divers are taking digital images of the wreckage before the vessel is raised and can be examined, National Transportation Safety Board member Jennifer Homendy said Wednesday.

Homendy described the investigation as lengthy and detailed. Investigators interviewed four crew members and Glen Fritzler, the owner of the company Truth Aquatics that operated the Conception. More interviews will be conducted with first responders, additional Truth Aquatics employees and the owners of the Grape Escape — the fishing boat that helped rescue crew members.

“I characterize these as very cooperative,” she said of Wednesday’s interviews.

She also met for two hours with the families of those who died in the fire.

“They’re the most important people to us right now,” Homendy said.

On the docks nearby, Homendy, Coast Guard Capt. Jason Neubauer and investigators toured the Conception’s sister ship, the 80-foot Vision, also owned by Truth Aquatics.

Though slightly larger than the Conception, the Vision has a similar layout. Single and double bunks are stacked two and three high in the boat’s sleeping quarters below deck. A wooden staircase leads from the sleeping area up to the galley. Authorities say that exit on the Conception — along with an escape hatch that opens up near the dive deck on the boat — were blocked by fire. NTSB shared a photo on Twitter earlier of Homendy and Neubauer packed inside a room surrounded by bunk beds, similar to the space where Conception passengers would have been when the fire occurred.

“I wanted to lay eyes on the vessel and just get a sense of the layout,” she said.

A day earlier, roughly a dozen agents with the FBI’s Evidence Response Team also boarded the Vision to snap photographs of the vessel’s interior, decks, staircases and entryways. They pinned sheets of paper with block letters beside some parts of the boat — an “A” next to a life preserver, a “B” next to the door to the top deck — and took pictures from several angles.

Neubauer said that four of the five crew members were tested for alcohol and, according to Homendy, tested negative. Drug testing results are still being processed.

NTSB is awaiting documentation pertaining to the vessel maintenance and training records, manuals, inspection reports, 911 recordings and licensing information. Neubauer said the Coast Guard and Truth Aquatics reached “a mutual decision” to not operate the company’s other two vessels during the initial investigation.

Neubauer said that although some passenger vessels are required to have a sprinkler system installed, federal regulations did not require that for the Conception.

Homendy said the federal agency started its investigation Tuesday morning into the cause of the fire, just after Coast Guard crews announced they would stop searching for passengers who were trapped below deck when the fire broke out. The rescuers have said there are no signs of additional survivors.

“This was a terrible tragedy,” Homendy said Tuesday. “I cannot imagine what the families are going through.”

The team of 16 investigators, which specialize in engineering, operations, survival factors and fire prevention, will be on site for seven to 10 days. They will work closely with the Coast Guard and first responders, Homendy said.

The NTSB could release a preliminary report within 10 days of the incident, but a final report could take two years.

Tyler McCurdy, supervisor of the FBI’s Ventura office, said that the FBI’s Evidence Response Team will gather evidence on behalf of the NTSB and the sheriff’s office. He would not specify the type of evidence they are collecting.

Homendy said she is “100% confident” that investigators will determine the cause of the fire.

If investigators uncover safety issues, the agency will issue immediate recommendations to protect the public from similar accidents, she said.

Marjorie Murtagh Cooke, former director of the NTSB Office of Marine Safety, said in an interview with the Los Angeles Times that investigators will try to answer several key questions, including why no one below deck was able to escape the flames.

“Vessels have to have two exits for escape by law for the sleeping quarters,” Cooke said. “It appears that both exits from the sleeping quarters bring you up inside the vessel.”

If both escape routes from the sleeping quarters lead to the same area, which appears to be one large room, a fire there could potentially block the only means for passengers to get out, she said.

“With 30-plus people dying, the investigation could lead to changes in the way vessels are designed or protected depending on the findings,” she said.

The deadly fire has rattled Santa Barbara residents, many of whom have ties to the tight-knit maritime community.

The region has been hit with back-to-back tragedies over the last several years, residents say. First, the Thomas fire charred 281,893 acres in Santa Barbara and Ventura counties in 2017. Then, last year, a devastating mudslide tore through Montecito, destroying homes and killing at least 21 people, in Santa Barbara County’s tony enclave. Now, the deadly fire on the Conception.

Don Barthelmess, a retired diving instructor who taught at Santa Barbara City College for 30 years, said he has chartered the Conception many times over the years. He was most recently aboard its sister vessel, the Vision, in May. At that time, the crew explained the safety procedures and pointed out firefighting equipment, Barthelmess said.

“(The captain) trained his crew very well. They took their training very seriously. They’re very serious about boat briefings,” he said. “I can’t think of a situation where it’s been lax. I know that that crew would do everything humanly possible to try to save people if they could have.”

Perry Cabugos, who previously worked as a second captain on the Conception and as a captain on the company’s other boats, said divers frequently sought out Truth Aquatics’ vessels for trips with their friends and families.

“We’ve seen generations come through,” Cabugos said. “You’d see them come back year after year with their families and watch their kids do their first dives. The dive community is a family.”