Search and recovery operations ended in the early morning of Wednesday for victims of the worst fire in Oakland, a city in northern California, on the U.S. west coast.

The death toll stood at 36, unchanged since Monday, as agents from the U.S. federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) were continuing their investigation into cause of the fire on Friday night.

"ATF is looking at every possible source of ignition," said ATF special agent Jill Snyder. "There is no timeline for the conclusion of the investigation. ATF experts will be on scene for possibly several more days examining physical evidence. The analysis of data and interviews may take several weeks."

The fire occurred in a two-story structure, named "Ghost Ship" by Derick Ion Almena, the man who turned the warehouse into the site of an arts collective, a residence for his family and reportedly some other tenants, and an underground party venue.

"By all accounts, the fire started on the first floor," Snyder told reporters on Wednesday morning. "There were two internal stairwells from the second floor that led to the first floor. Neither went to an exit. Smoke traveled up the stairwells, trapping the people on the second floor. There was rapid fire progression. Initial witness interviews have indicated the fire was well developed by the time the second floor occupants realized a fire was going on."

Her evaluation echoed what spokesman J.D. Nelson of Alameda County Sheriff's Office told a press conference on Tuesday, that autopsies had revealed the victims died of smoke inhalation and not burns.

Before winding down the search operations, which had involved about 300 firefighters since around 11:30 p.m. Friday, a secondary search by recovery personnel and cadaver dogs was made and returned no additional victims.

While fire crew and heavy machinery were gone, few workers remained after midnight to remove debris from the warehouse. Also remained were shrines put up by mourners with flowers, candles, notes and others along sidewalks leading to the structure.

At 1:00 a.m., a young couple came up at one of the shrines. The woman wrote a few lines on a book there, about her prayers for the dead; and the man said he knew somebody among the victims through a friend.

At the time of the fire, an electronic music party was going on, supposedly from 9 p.m. to 4 a.m.

Oakland Fire Chief Teresa Deloach-Reed said on Saturday there was no sign of fire alarms and no evidence of a sprinkler system.

On Tuesday night, Oakland Mayor Libby Schaaf announced the release of the permit and complaint history from the past 30 years from the city's Planning and Building Department related to the warehouse.

By Wednesday morning, the Alameda County Sheriff's Office Coroner's Bureau has identified 35 of the 36 victims, mostly Californian residents in their 20s and 30s, and notified 32 families.

At an additional press conference on Wednesday afternoon, Snyder cautioned about speculations in media reports, saying there was no evidence that a refrigerator was the origin of the fire, and neither was arson.

"The digging part of the investigation is done, now is the analysis part," said Snyder.

source: Xinhua