I Prefer Them Alive Trophy in Resident Evil 6

During Chapter 2 - Leon's Campaign, you will enter a cathedral. In here, you will have to complete a set of puzzles in order to open the secret passage behind the altar. Once you do this, a new B.O.W - the Lepotitsa - will emerge. In order to get this, you simply need to kill him faster than he can kill the civilians. Use heavy weaponry such as shotguns, rifles or explosives, and if on a second playthrough, magnums. If you're having difficulty with this, then playing on Amateur is recommended. If playing in co-op, both players will receive this. If done correctly, this will unlocking during the cutscene, or after it.

For a video demonstrating this method, please see below. Credit to PowerPyx for the video.