"The fire was intentionally set using an ignitable liquid," Hoover said.
Firefighters were called to a fire at 114 N. Church St. at about 8:30 a.m., Hoover said. The fire quickly spread in both directions to the other side of the duplex at 112 N. Church St. and to a house next door at 116 N. Church St.
The duplex was vacant because a previous fire in November displaced the former residents, Hoover said. The home at 116 N. Church St. was being lived in, but the owner wasn't home.
Hoover said the fire damaged about 50 percent of the home at 116 N. Church St. He said the fire caused about $150,000 in damages to both structures.
One firefighter was treated and released from the hospital for a minor eye injury, Hoover said.
Anyone with information can call the Martinsburg Fire Department at 304-264-2111, the Martinsburg Police Department at 304-264-2100, or Crime Solvers at 304-267-4999.
— By Dan Dearth