Why doesn't the supposed killer recognize Walter when he went to jail to talk to him? After that scene, we later see that Walter went to college with him and they make eye contact at one point. So, I'm assuming that the falsely accused guy would have some memory of Walter...
In The Number 23, Walter does go and see Kyle Flinch the supposed killer in prison. Walter and Kyle talk there. As for the College or University Walter and Laura Tollins (the victim) attend at no time in the movie is it shown or suggested they attend the same class.
Walter looks through a window in the door of Laura's class where he witnesses the hand touching of the professor (Kyle Flinch) and his (Walter's then) girlfriend, Laura. Kyle does not see or acknowledge Walter at this point. The eye contact happens between Walter and Laura.
Laura and Kyle then go on with a relationship whilst Walter stalks and watch's from the shadows and such unseen. In a place as large as a school I can see no reason for Kyle to remember Walter, especially if they had no class together. Even if he had seen Walter in passing Walter would have been 15 years younger.