"A privateer working for the Templars as a fence is believed to be hiding in Havana's poor district. Locate and kill him."
Approach the Restricted Zone from the West. Immediate duck into the Stalking Zone found there. Use Eagle Vision to locate your target. He walks a short patrol between the hiding spot and the drunken pirates nearby. Just wait for him to get close to gank him from the Stalking Zone or the hiding spot. Whistling helps to ensure you get him.