Dallas Fire-Rescue says investigators are looking for the arsonist who tried to torch a leasing office in Old East Dallas before dawn Tuesday.
The automatic fire alarm sounded at a 12-story building in the 4100 block of North Central Expressway, just south of Fitzhugh and U.S. 75, just before 5 a.m.
Firefighters arrived to see smoke coming from the first floor, and called for more units because of the size of the building.
As firefighters went inside they discovered the building's automatic sprinkler system had put out the fire, according to Dallas Fire-Rescue.
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After firefighters took care of the remaining hot spots, investigators said they found "an incendiary device" had been thrown through the window of the first-floor leasing office.
No one was in the office at the time of the fire.
One firefighter suffered a "musculoskeletal injury" and was taken to the hospital for treatment according to Dallas Fire-Rescue.
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Fire investigators are looking for who started the fire and why.