The guard was walking around his patrol, bored and almost hoping that something was going to happen just so he had something to do.
He got a little bit more than he wanted.
Out of the corner of his eye he saw a tiny flash on the side of the hill and almost before he could register it a searing pain came from his neck as the bullet passed through his jugular. Out of the other side the bullet came, along with a fine mist of blood, neck bone, nerve and voice box. Then the blood came. It drenched the wall and, the sniper noticed, went just around the corner.
The corner that the next guard was coming around as he completed the circuit.
The sniper had to act quick as he realised the guard would raise the alarm. He had to be killed. The sniper repositioned himself and aimed quickly. He went for the jugular and pulled the trigger.
He hit the chest.
The man cried out as he was hit, and unfortunately this distress signal was heard by another guard in the compound and this guard raised the alarm. At the most critical stage in the operation.