Trust Your Eyes - Linwood Barclay

Thomas Kilbride is a map-obsessed schizophrenic so affected that he rarely leaves the self-imposed bastion of his bedroom. But with a computer program called Whirl360.com, he travels the world while never so much as stepping out the door. He pores over and memorizes the streets of the world. He examines every address, as well as the people who are frozen in time on his computer screen. Then he sees something that anyone else might have stumbled upon—but has not—in a street view of downtown New York City: an image in a window. An image that looks like a woman being murdered.
Thomas's brother, Ray, takes care of him, cooking for him, dealing with the outside world on his behalf, and listening to his intricate and increasingly paranoid theories. When Thomas tells Ray what he has seen, Ray humors him with a half-hearted investigation. But Ray soon realizes he and his brother have stumbled onto a deadly conspiracy. And now they are in the crosshairs.