Why does the sniper kill the old woman?

In this story, the sniper shoots the old woman because she
is an informer.  He shoots her because she is trying to get him
killed.

At the point in the story where he shoots her, an
armored car has just appeared, carrying police.  The old woman talks to one of the men
in the car.  She points up to where the sniper is.  The man looks out, the sniper shoots
him.  Then he shoots the woman.

Even though the woman is
from his neighborhood, she is an enemy if she is going to tell the police where he
is.