After
The weapon will scan the area, revealing Okro 'Vagaduun to the southwest. Grab a Battle Rifle or other mid to long range weapon, and go there. (you can't take the scorpion)
Okro is protected by grunts, Jackals, and on Normal difficulty, one other elite. He himself has only an upgraded energy sword and invisibility. The Terrain will give you the high ground, so stay up there, and pick off his guard. Once the others are dead, throw fusion coils at the area to reveal his invisibility. Shoot until he's dead, too. Killing him will trigger a wave of high ranking brutes. Defeat the brutes to unlock this achievement.