Flames of Murder

Gun stores torched and the store owners burned alive.
Who would do something this horrible?
What do they have to gain?
Flames from a torched gun store bounce across the rooftop, consuming everything in its wake.
With the heat from the fire, bullets fly through the night air as the firestarter watches the scene. This is his first.
FBI Agents Mac and Spencer join a task force with ATF and an Atlanta PD fire investigator to stop the gun store torcher. The fires demolish stores and burn people alive as the firestarter feeds a need.
How many stores will he torch before he's stopped?
How many people will he murder?