On Killing by LtCol Dave Grossman, 2009, Excerpts
Close range involves any kill with a projectile weapon from point-blank range extending to midrange. At close range the resistance to killing an opponent is tremendous. When one looks an opponent in the eye, and knows that he is young or old, scared or angry, it is not possible to deny that the individual about to be killed is much like oneself. It becomes extremely difficult to deny their humanity.
At this range the interpersonal nature of the killing has shifted. Instead of shooting at a uniform and killing a generalized enemy, now the killer must shoot at a person and kill a specific individual. Most simply cannot or will not do it. Even when the killer has every motivation to hate and despise his victim, and every reason to quickly depart his close-range kill, he is often riveted, frozen by the magnitude of what he has done.
At close range, soldiers experience a brief, fleeting, and not often mentioned feeling of elation upon succeeding in killing the enemy. This euphoria stage is almost instantly overwhelmed by the guilt stage as the soldier is faced with the undeniable evidence of what he has done. At this range the screams and cries of the enemy can be heard, adding greatly to the extent of the trauma experienced by the killer. The guilt stage is often so strong as to result in physical revulsion and vomiting.