Three months after a fire swept through the upper floors of the landmark Marco Polo condominium in Moiliili, killing four people and causing more than $100 million in damage, city officials still cannot say precisely what caused the largest structural fire in Honolulu history.

The official incident report released Monday ruled out arson, natural causes and rumored reasons, such as a drug lab accident. But the 85-page report left many questions unanswered, including chiefly what caused the fire.

Anthony Quintano/Civil Beat

Speaking in somber tones during an hour-long news conference at the Honolulu Fire Department’s McCully-Moiliili Fire Station, Mayor Kirk Caldwell acknowledged the four people who died, three in the fire and a fourth weeks later in the hospital, and said he hopes that the city can learn from the incident.

He also expressed gratitude for the more than 130 firefighters who responded to put out the fire, many rushing in the burning building to evacuate residents.

“I believe that because they did their jobs, lives were spared,” said Caldwell, who was joined at the presentation by Honolulu Fire Chief Manual Neves and Fire Battalion Chief Jeff Hooker, who led the investigation.

“We can never bring back those who perished, and our hearts continue to go out to their families,” Caldwell added. “But what can we learn?”

In the end, Caldwell said, as much as the city and Honolulu Fire Department investigators wanted to say what caused the fire, the investigators had to classify the fire’s cause as “undetermined.”

Cory Lum/Civil Beat

Still, the officials were able to say where the fire started, how it spread, and what might have caused it. According to Hooker, the fire appears to have started in the living room of unit number 2602 on the building’s mauka side, which faces Manoa Valley.

Hooker said several items drew their attention as possible causes, including standard 110-volt wall outlets, a 220-volt air conditioner outlet, air conditioning, small gas fuel cylinders used for craft projects, a lighter, and a laptop and desktop computer. Another subject of concern is that at least one of the occupants was a smoker.

Any of these could have caused the fire, Hooker said.

But he added that exact cause was unknown. “We can’t pinpoint it or say this is what caused this fire.”

Cory Lum/Civil Beat

The report quotes the apartment’s occupant as saying he saw a plume of smoke rising from the floor in the living room and shoot up to the ceiling followed by “what sounded like a whooshing sound, then fire appeared.”

Fire inspectors identified the gas cylinder and wand-type lighter as the possible ignition sources, but the occupant said they were not being used at the time.

In any case, once the fire started, winds sweeping from Manoa toward the ocean blew the fire like a blowtorch across the hall to the makai said of the building, Neves said. The units with the fatalities were on the makai side across the hall from the unit where the fire started, Neves said.

The seven-alarm fire sent a column of smoke billowing from the iconic Marco Polo building, which overlooks Ala Wai Community Park and Waikiki.

The fire started on a Friday afternoon and blazed for hours, creating an alarming image for the throngs of people traveling in and out of Manoa, Moiliili and Waikiki.

The blaze prompted debates about whether Honolulu’s fire safety ordinance was adequate to protect the thousands of Honolulu residents who live in Oahu’s high-rise towers.

Anthony Quintano/Civil Beat

Although the fire’s cause remained undisclosed, there was widespread agreement that a sprinkler system could have limited the damage.

The fire safety ordinance doesn’t require sprinkler systems to be added to buildings built before 1974, including the Marco Polo, which was built in 1971. According to the Honolulu Fire Department, there are 358 high-rise residential condominiums and hundreds of other residential buildings over 75 feet tall that do not have fire sprinkler systems.

Nonetheless, the question whether the City Council should require older buildings to install sprinklers has been vigorously debated. Although Caldwell has proposed a bill requiring sprinklers in older buildings, the Residential Fire Safety Advisory Committee, formed by the City Council in August, still is exploring options.

Caldwell said a proposed solution is expected by the end of October.