In The Sniper why did he shoot the unarmed woman

The sniper shot the unarmed woman because she exposed his position on the rooftop.

Then round the corner of a side street came an old woman, her head covered by a tattered shawl. She began to talk to the man in the turret of the car. She was pointing to the roof where the sniper lay. An informer.

The turret opened. A man’s head and shoulders appeared, looking toward the sniper. The sniper raised his rifle and fired. The head fell heavily on the turret wall. The woman darted toward the side street. The sniper fired again. The woman whirled round and fell with a shriek into the gutter.