Early in Chapter 1 you will reach an open area with 4 patrolling/stationary officers and 1 commander. This is just before needing a charge to blow the door. The commander in the middle and all 4 officers, once they stop moving, will have their backs to you. Sneak up behind the commander and use R3 to stealth kill him. Get yourself killed or reload the checkpoint to repeat this process 4 more times to earn the perk.