In "The Sniper", how does the plot of the story build suspense?

Clearly suspense is a very important element in this short
story. From the very first paragraph the suspense that keeps us reading builds until we
reach the shocking ending of this tale. Note how this is
achieved:

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Around the beleaguered Four Courts the heavy
guns roared. Here and there through the city, machine guns and rifles broke the silence
of the night, spasmodically, like dogs barking on lone farms. Republicans and Free
Staters were waging civil
war.

This description does
much to paint the scene for us: as we read on we are plunged in to a civil war where
brother fights brother across the rooftops of the city. Then we are introduced to the
main character - a Republican sniper who is lying on a rooftop. Note what is said to
us:

He paused
for a moment, considering whether he should risk a smoke. It was dangerous. The flash
might be seen in the darkness, and there were enemies watching. He decided to take the
risk.

Note how the author
builds up the suspense here by telling us about the potential dangers of the simple
action of lighting a cigarette before the sniper does so. This thus sets the reader on
the edge of his or her seat as we wait to see what happens when he lights his cigarette.
The gun shot that occurs as a result thus shocks us but also raises suspense in turn as
we discover that there is a sniper on the opposite roof trying to kill the main
character. This thus makes us wonder who is going to survive this urban battle of wits
and come off the roof.

Suspense then can be said to be
sustained through the setting and the description, but most importantly the way that the
author describes the potential dangers of the situation the character finds himself
in.