Memory Man by David Baldacci (2015)

Looks like we have a new Baldacci character - Amos Decker. This is his back story. Amos was a football player that got one play in the pro's when he was hit so hard, he died twice on that field. When he woke up he was a savant and had acquired a perfect memory - remembering every detail of what he saw and experienced, plus seeing things and numbers in colors. He met his wife while he was recuperating, and she always kept him sane. But with his wife and daughter murdered, he can't keep it together and for a while becomes homeless. He is pulled back into detective work when someone confesses to the murders months later, but he then goes on to solve a complex school shooting.