The Burning Wire by Jeffery Deaver

The weapon is invisible and omnipresent. Without it, modern society grinds to a halt. It is electricity. The killer harnesses and steers huge arc flashes with voltage so high and heat so searing that steel melts and his victims are set afire.
When the first explosion occurs in broad daylight, reducing a city bus to a pile of molten, shrapnel-riddled metal, officials fear terrorism. Rhyme, a world-class forensic criminologist known for his successful apprehension of the most devious criminals, is immediately tapped for the investigation. Long a quadriplegic, he assembles NYPD detective Amelia Sachs and officer Ron Pulaski as his eyes, ears and legs on crime sites, and FBI agent Fred Dellray as his undercover man on the street. As the attacks continue across the city at a sickening pace, and terrifying demand letters begin appearing, the team works desperately against time and with maddeningly little forensic evidence to try to find the killer. Or is it killers . . . ?