Well, there are plenty of very visual elements in this great story. You might like to think of how you would stage it as a film to help you think through this question. For me, in addition to the scene at the end, I would have to pick the part where the sniper successfully tricks his enemy by dropping his rifle, and then is able to see him on the opposite roof, and hears him lighting a cigarette. This of course comes before he kills him.
For me, the easiest incident to visualize would be right at the end, when the sniper looks at the dead man and sees it's his brother. You could bring at least three senses into play here. The guy sees his brother -- you could describe visually what his brother looks like having been shot and then falling off the roof. You could describe the tactile sensations of lying on the pavement, looking at the corpse. You could describe the sound -- silence after the machine gun stopped, then maybe a roaring in his ears (at least I've had that sound when I've had a huge shock).