This can be done in the mission “The Final Test”. You can easily combine both trophies.
Step 1: From the start sneak through the area on the left side and you will see a pipe at the end of the building.
Step 2: Wait until the two mechanics pass by the pipe or else they will see you. Climb the pipe as soon as they walk into the building. Enter the room on the upper floor through the window.
Step 3: Place your pistol on the floor by the door (press triangle / Y in the inventory to drop it). This unlocks the Security defeated trophy and will distract the guard.
Step 4: Now the guard goes away with the weapon and the target will be alone in the room with you. Take him out and hide the body in the bathroom box.
Step 5: Go back the way you came, throw coin to distract the guard underneath the pipe.