"A group of outlaws is responsible for a rash of violence and mayhem in the city. They often congregate in the swamps just outside the city. Kill their leader and end their attacks."
Head to the Viewpoint/Fast Travel location and synchronize with it if you haven't already. This makes for a fine starting point for this hunt. Immediately turn around and hit the sentry. After that locate your target below you, a Brute. Wait for the Berserk dart to wear off and kill him. If you are quick enough, an aerial assassination is an option.. Be sure to take a moment to deal with that scout you tagged with a dart not long ago too.