CHICAGO (AP) -- Fire officials say a blaze that killed two Chicago firefighters earlier this week was caused by wood or rubbish that was started on fire.
The fire at a vacant building on the city's South Side appeared to have been started by an open flame ignition. That's according to the Chicago Tribune.
Fire officials tell the newspaper that they don't know what the intent was of anyone responsible for starting the fire.
The Chicago Police Department's bomb and arson unit is investigating.
Fire officials didn't immediately have further information when reached Friday.
Two firefighters died Wednesday after a roof collapsed onto them. Firefighters Edward Stringer and Corey Ankum had been searching the burned, vacant building to make sure no vagrants were sheltering inside.
Fire officials say no civilians were found inside.