By Daina Beth Solomon
LOS ANGELES (Reuters) - Investigators of a suspicious fire that destroyed an apartment complex under construction in downtown Los Angeles began walking the site on Wednesday looking for clues to origins of the blaze, two days after it reduced a city block to charred ruins.
Firefighters were still working to extinguish hot spots in the rubble on Tuesday, and it took another day before the area was cool and safe enough for inspectors from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives and city fire department to enter.
A national ATF squad is taking the lead in the probe, as it has with only one other Los Angeles fire this year, city fire department spokesman Peter Sanders said.
ATF special agent Tom Mangan told reporters he expects the agency's team of 50 investigators will reach a preliminary finding in seven days.
At that point, he said, the blaze may be ruled either an arson or an accidental fire.
Fire officials have said they were treating the blaze, which erupted shortly before 1:30 a.m. local time on Monday, as a "criminal fire," citing the size of the conflagration, as well as the speed and intensity with which it spread.
As of Wednesday, however, investigators said they still lacked evidence that the fire was intentionally set.
The site that burned - two stories of poured concrete beneath five floors of wood framing - occupied a whole city block near the junction of two major freeways.
Moments after the first alarm, firefighters whose station is located at the end of the block emerged to see the entire development engulfed in flames, fire officials said.
"A building in the middle of the city burning at 1 o'clock in the morning is suspicious," said Carlos Canino, special agent in charge of the ATF's Los Angeles office. "We're looking for signs. It could be arson, it could not be arson."
Most of the structure that burned collapsed in a twisted pile of blackened lumber and scaffolding, producing heat so intense that it ignited three stories of an adjacent office high-rise and blew out windows in that building and two others.
One major freeway into town was shut down for several hours, along with three key off-ramps of another, gridlocking traffic in the heart of the nation's second-largest city through Monday's morning commuter rush.
No injuries were reported. Canino put estimated property losses at $10 million to $20 million.
(Writing by Steve Gorman; Editing by Eric Walsh)