The Phantom Bullet

A Gun shot, Murder and Police interrogations. Johnny was the sole eyewitness to his friend’s murder. He desperately wanted to help the police prosecute the killer, but he had no memory for ever seeing the culprit pull out the gun or shoot. Over the course of several weeks he was interviewed repeatedly by the police - pushing him to remember details of the crime that he never saw; and over time his memory began to change, to the point where he developed a detailed false memory for seeing the crime go down. How did this happen?