In you motel room, pull out the next origami figure, which tells you to kill a man. You'll grab your gun and head to the target's house. Knock the door and when the man answers, either perform the combo instructions, or knock on the door again after he slams it in your face. You'll pull out your gun and walk into the apartment, the drug dealer giving way as he retreats to a side room. When he gets in there he'll pick up a shotgun and a chase will take place, consisting of a long quicktime sequence as you run through the house trying not to get shot. If you fail the sequence, the guy will kick you out and you won't have a chance at either of the Shark trophies.
If you are successful at the quicktime sequence, he'll chase you into his daughters' room where he'll find he's out of ammo. He'll tell you about his little girls before going down on his knees to beg for mercy. This is the decision point for you, and whether you choose to pull the trigger with or not, you'll get one of the trophies. Like all trials, failing gets you nothing and succeeding earns you more letters to the address where Shaun is being held.