Fire Marshall Mike Martin confirmed that the cause of the fire is arson, and that an accelerant was not used.
Firefighters were called to the boarded-up school around 7 p.m. and the fire was contained in about 15 minutes.
Fire Marshall Mike Martin said they are looking for four suspects--young black men, last seen fleeing the scene around 7:30 p.m.
The school, located at 1611 31stStreet, near Oakwood Cemetery, has been closed since 2004.
The school shut down after Armstrong merged with Kennedy High and moved to nearby Cool Lane. Police later used the old building for training, but investigators tell me it’s been mostly empty since 2008.
“It's been vacant for some time,” said resident Norman Farrington, who lives across the street and captured video tonight. “We occasionally see police training there, but it's been pretty vacant since."
The fire damage was contained mainly to the first floor, with some water damage on the second, said officials.
People living in this area, say the power to the building was shut off years ago.
By Monday evening, no dollar estimate of the damage was available.
Sources also said that they are investigating for connection with the mayhem that occurred late Saturday night at 31st and R Streets in Church Hill.
Police ask for anyone with information to call Crime Stoppers at 780-1000.