Trepang2

This achievement can be achieved on any squad in the game, but I found where I did it to be the easiest to complete.

Right at the beginning at Jorvik Castle, you are greeted by your team and a weapon cache with the suppressor upgrade for the sniper rifle and the rifle itself. Attach the suppressor to the rifle and head to the window with your guys as they are waiting for your shot. There are 6 Cultists in the courtyard all spread out pretty well, but mainly mostly out of eyesight of each other. First, find all 6 and wait for them to spread out in their patrol routes and fire when ready. (trust me use the slow-motion ability to make it easier)

*Little disclaimer I wish I knew beforehand. Don't use a laser sight on the rifle as it will alert the guards that they're being looked at. Guards do not react directly to their guys dropping and will walk up to confirm which gives some time to salvage a situation, and if you miss a shot on a guy you have a second to land another hit or everyone immediately gets pissed.