"Antonio Rueda - a Templar associate - is trading weapons and explosives in Havana's trade district. Find him,end his business ... and his life."
Head over to the Southeast corner of the Restricted Zone. use the group of Dancers there. Head into the West and send the Dancers to distract the Guards just a bit West from you. Climb over the door nearby and into the Restricted Area. Stay on the low roof ahead of you. Stay here and use Eagle Vision to locate your target. When he is in range, tag him with either a pistol or a Berserk dart. Just leave the area after that.