LOS ANGELES (AP) — Crews were dousing hot spots and tearing down unsafe sections of an unfinished downtown apartment complex Tuesday, a day after a fire reduced most of it to a block-long wall of charred timber.

Smoke still rose from the ruined Da Vinci complex more than 24 hours after it caught fire. Firefighters hosed down the blackened debris and a private contractor used heavy equipment to knock down some scaffolding.

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Arson experts were unable to enter the building until it was declared safe. The Fire Department requested federal help, and agents of the Bureau of Alcohol, Tobacco, Firearms and Explosives were expected to arrive Wednesday, a Fire Department statement said.

Fire officials said they suspect arson because the blaze erupted so quickly over so much of the building.

“It’s very rare for the entire building to be engulfed at once,” city fire Capt. Jaime Moore told the Los Angeles Times. “There may have been foul play.”

Investigators will interview witnesses, check security camera and personal video of the fire, and will use dogs that can sniff fire accelerants.

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The fire, which engulfed the wooden framing of the seven-story building, caused an estimated $10 million in damage, Moore said.

Another $1.5 million in damage was done to a freeway where a sign melted. Traffic-monitoring fiber-optic cables under the pavement may have to be replaced, authorities said.

The intense heat also damaged three nearby office high-rises.

A block away, the city Department of Water and Power reported cracks in at least 160 of the 10-by-4-foot windows at its headquarters.

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The burned apartment complex was planned to be a 1.3-million-square-foot residential building — one of a series of large complexes that have gone up around downtown in recent years.