ESCONDIDO -- An investigation into the massive fire that destroyed four downtown condo buildings Thursday will continue this week as investigators comb through piles of charred wood and rubble for some sign of what sparked the blaze, authorities said.

There was nothing new to report by Sunday, said Carol Rea, a spokeswoman for the Escondido Fire Department, which is leading the investigation into the blaze that leveled The Paramount complex on Escondido Boulevard near Washington Avenue. Authorities are also continuing interviews with witnesses and workers at the complex, she said.

Investigators are looking for remnants of tools or other things that may have started the fire, and are trying to eliminate sources and determine whether the blaze was accidental, electrical or even natural, which seemed unlikely, authorities said.

The city's police department and the Bureau of Alcohol, Tobacco, Firearms and Explosives are aiding the investigation, Rea said.

The huge, twisted piles of blackened debris that lay where the 122-unit complex was to stand will remain in place until the investigation is complete, Rea said.