Accelerant was used to stoke the massive DaVinci apartment fire downtown, officials with the U.S.  Bureau of Alcohol, Tobacco, Firearms and Explosives said today.

The revelation came as the amount of prospective rewards for information leading to the arrest and conviction of any suspect in the case reached a rare $170,000. Officials with the ATF, Los Angeles Fire Department, and city of L.A. announced the reward amount at a press conference today.

A spokeswoman for the ATF told us agents were not specifying what kind of accelerant was used. But the presence of some type of malicious fuel for the fire would explain how the blaze seemed to erupt throughout the seven-story building almost instantaneously Dec. 8.

Evidence of accelerant indicates this wasn't just a kid playing with matches. It suggests whomever did this was serious about wreaking havoc.

The arson fire that destroyed an under-construction portion of the DaVinci apartment complex drew one-third of the city's on-duty firefighters, 250 in all, and could be seen for miles.