A Man Out Walking His Dog

Norman,a retired train driver,who has been left by his wife,is becoming increasingly eccentric in his solitude. Regular walks with his faithful companion Sammy the spaniel keep him sane. They both love being out in Nature,but a walk along the local river turns tragic when they discover a young woman's body. He does the decent thing and recovers the corpse. This leads to him being arrested by an over-zealous detective who suspects that he made the attack on the victim. How can he prove his innocence,and why do witnesses place him at the scene - does he have a double ?