86fb992a_Grand_Theft_Wiki__the_GTA_wiki__Reward_for_sparing
[Mission] Portrait of a Killer [Target] Gunman [Description] There are a lot of gunmen in the parking lot that have to be killed. One of these, usually the one near the corner next to Dukes Boulevard, will drop his weapon and raise his hands if you kill all of the other gunmen. Niko can shoot him to kill him or just walk away to spare him. This doesn't have any repercutions later in the game and is probably just a way to add a special touch to the mission. [Reward for sparing] 
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Choices in GTA IV - Grand Theft Wiki, the GTA wiki