Close range.
A ...kill with a projectile weapon from point-blank range, extending to midrange. The key factor in close range is the undeniable certainty of responsibility on the part of the killer.
A typical case by an Israeli paratrooper from 1967:
"We looked at each other for half a second and I knew that it was up to me, personally, to kill him, there was no one else there. The whole thing must have lasted less than a second, but it's printed on my mind like a slow motion movie. I fired from the hip and I can still see the bullets splashed against the wall about a meter to his left. I moved the Uzi, slowly, slowly it seemed, until I hit him in the body. He slipped to his knees, then he raised his head, with his face terrible, twisted in pain and hate, yes such hate. I fired again and somehow got him in the head. There was so much blood . . . I vomited, until the rest of the boys came up."
Similar to midrange the killers have euphoria and elation but it's a very short period which is suppressed by overwhelming guilt and remorse sometimes with physical reaction (like vomiting). Beside the visual they also hear the screams and cries. Sometimes the kill isn't instant so they there to witness their extended agony. Sometimes the killer even tries to comfort the victim.
Major General Frank Richardson told Holmes that "it is a touching fact that men, dying in battle, often call upon their mothers. I have heard them do so in five languages."
A ranger remembers: "Later I walked over to take another look at the VC I had shot. He was still alive and looking at me with those eyes. The flies were beginning to get all over him. I put a blanket over him and rubbed water from my canteen onto his lips. That hard stare started to leave his eyes."
But of course on this range the resistance to killing an opponent is tremendous. [...] It is here that many personal narratives of nonkilling situations occur.
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.