You can do this a little bit faster in the first level as well. When you reach the point where you find your first ammo crate (the game will inform you of this) you'll come to a room with three guards. You're best off dying initially to trigger the pattern. Once the area resets, sprint to the drop off and press B without touching the sticks. You should be able to kill the first guard without alerting him then sprint and kill the second guard. The third guard will kill you resetting the area again for two more quick kills. Happy hunting