You can reload checkpoints to keep killing the same few enemies with throwing knives repeatedly to knock this one out. I did this against the first few enemies on the Bandits level via the checkpoint reload method. Select throwing knives from your equipment menu and use
to throw them.
Check out the video below for a full playthrough of the game showing all collectibles, miscellaneous achievements like this one, and the Moral Points I obtained (I skipped a lot of them) in order to get the Redemption achievement. The Bandits mission starts at timestamp 53:16
. I kill the first couple guys with throwing knives in the video, showing how easy it is to do here.