A man has been arrested on suspicion of starting a massive inferno that destroyed an unfinished apartment building and damaged adjacent office towers in downtown Los Angeles, authorities said.

Dawud Abdulwali, 56, of Los Angeles, whose name may be an alias, was arrested Tuesday on a traffic warrant and only later was booked on suspicion of aggravated arson and arson of a structure, potential charges that could lead to a life sentence, fire officials said.

He was being held Wednesday on more than $1 million bail and was expected to be charged on Thursday.

The arrest culminated a six-month investigation involving the Los Angeles Fire Department, LAPD and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, but officials would not say what evidence led them to Abdulwali.

Investigators believe he acted alone and had no connection to the complex that burned, said Carlos A. Canino, special agent in charge of the ATF Los Angeles Field Division.

Abdulwali was renting a room in South Los Angeles last year, his landlord, Poleth Chavez, told the Los Angeles Times. In December, around the time of the fire, he paid two months' rent up front and left, saying he was heading to San Francisco.

"He's pretty quiet," Chavez said. "He keeps to himself."

The Dec. 8 fire gutted the 1.3-million-square-foot Da Vinci complex that was in the wood-framing stage, sending up flames that could be seen from miles away.

The fire's heat cracked or shattered hundreds of windows in neighboring buildings, ignited small fires in one, and damaged an adjacent freeway. The complex's developer, Geoff Palmer, said at time of the fire that he intended to rebuild, but it's not clear where those plans stand.

Authorities declined to discuss details of how the suspect was identified, but Canino said hundreds of people spent thousands of hours on the investigation.

"Cutting-edge technology" and old-fashioned "wearing-out-the-shoe-leather" police work were involved, he said.

Mayor Eric Garcetti said the fire caused $20 million to $30 million in damage to the building site and another $50 million to $60 million to a city-owned building nearby.

Canino said that fire and the damage figure "could have been a lot worse."

"You know, different wind change, different atmospheric conditions, it could have been a $200 million fire instead of a $90 million fire," he said.