I'm currently writing a Walker attempted assassination / JFK assassination short story, and although it's going great, I need to be as historically accurate as possible. This is the only trouble I have regarding this.
Between pages 183-187 of the Warren Commission Report, photographs recovered from Oswald's possessions indicate that the assassin attempted to shoot General Walker at the rear of his house while behind a fence to rest his rifle on. This conclusion was reached by comparing the position in which the photograph was taken and the trajectory of the bullet that went through General Walker's window and into a wall.