In "The Sniper" what effect does war have on the sniper?

Liam O'Flahery's anti-war short story "The Sniper" is about a Republican sniper alone on a rooftop during the Irish Civil War. O'Flaherty writes from a detached point of view which provides only the physical facts of the story. The text never reveals the emotional feelings of the sniper, even in the shocking surprise ending. All the reader knows is the sniper gives a "smile" and a "cry of joy" when he is successfully kills.

The sniper is described as being "thin and ascetic." He is a "fanatic" who is battle hardened. He seems to kill easily and without hesitation. The reader must assume that he has killed often and, during the course of the story, shoots a woman and an armored car commander before matching wits with the opposing Free-State sniper on the opposite roof. 

He tricks his enemy by pretending he has been killed. He drops his rifle from the roof to bring his opponent out from cover. When the Free-State sniper reveals himself, the Republican sniper kills him with his revolver. The body falls to the street below and when examined, the Republican sniper sees that it is his brother. 

From the text, it is impossible to know if the sniper changes his attitude toward the war, even after killing his brother. The only word that reveals his nature is when O'Flaherty calls him a "fanatic." A fanatic is someone totally devoted to one cause. The sniper is obviously fighting for what he thinks is right. He kills his enemy indiscriminately and no remorse is shown. We don't know the details of why he and his brother were fighting on different sides and we can't know how the sniper reacts to seeing his dead brother on the Dublin street. All that can be said for sure is that war is a terrible thing which makes soldiers do things they would otherwise never dream of doing.