When you go do the mission "Backup for Brad" and you are in that spot where right in front of you is a railing, jump on to it and make sure you jump on the gray part.

Get on edge of the archway and there is the SMG. Equip it and go to the boxes.

Jump on it and jump a second time, then go up and get behind the wall.

Carlito will stop on the corner and shoot, but the bullets won't hit you. You need to shoot him with the SMG, then he will run to the brown wood floor.

Shoot him until he goes to the metal crossway. Jump up there and finally kill him.