The Witness

You walk up to the police officer. You ask him what has happened here. He tells you that someone was shot down mysteriously by an unknown sniper. A second later an unconscious officer lays on the ground. Horrified, you run away and sprint back up the hill. Your friend is still at the top of the hill. "What happened to you?" he says. Gasping for air, you sit on a tree stump and catch your breath. After taking a deep breath a few more times, you look at your friend. "I think I just witnessed a murder." you say. "What?!" he exclaimed.