Craft a Smoke Bomb with a large AOE Range, then go to the Southwest of the City (watch the Video for a exact Location)
This is also a good location to get the following Achievements:
If you fail just enter the Animus Island and go back in the City, the Guards should be back. Climb the archway, throw (if you want a cherry bomb to lure all guards to one spot) the smoke bomb and jump into the smoke, press x a few times.
Shinwasha: Tunnel Exit is Arcadius for people who want to know that.
Tazwaz: I was having the same trouble as everone then slightly changed my strategy and got it first try. I did everything the same as the video did and in the same location except instead of climbing the arch and juping down i did it all from the ground and changed my cherry bomb a bit by making it have the sticky pouch instead of the impact shell. making this change gives the bomb a fuse which gives you a few seconds to set, up change to your smoke screen bombs, and turn on your eagle vision then walk into the smoke and mash the x button while walking twords enemies ** do not hold right trigger because high profile kills take more time to exectute just walk and x button** HOPE THIS HELPS!!