You can easily obtain this trophy in the Prologue. The game requires you to plant a trip mine in a doorway before allowing you to proceed.
After shooting your target you must leave the building you are in and head back to the street where you planted the trip mine. When you see the truck pull up, shoot it's gas cap so you can snag a couple of quick kills. Wait about 10 seconds and you will hear an explosion. Some poor chum just walked into that trip mine that you set earlier! Enjoy your trophy!