SANTA BARBARA, Calif. — The National Transportation Safety Board says all six crew members were asleep when a fire broke out in a scuba diving boat off the coast of the Ventura County coast, killing 34 people.

The NTSB released a two-page preliminary report Thursday. Authorities have said they were investigating if there was a night watchman on duty at the time.

The report comes a day after divers recovered the remains of the last missing victim, one of dozens who were trapped below deck.

The Coast Guard has released additional safety recommendations in the wake of the Sept. 2 tragedy, such as limiting the unsupervised charging of lithium-ion batteries and the use of power strips and extension cords.

The FBI, Coast Guard and the U.S. Attorney's Office in Los Angeles are conducting a criminal investigation.