Deployed to Westside by Lt. Boyd to investigate local illegal activity, especially chems trafficking in the outer Vegas area, Ranger Keller is working undercover investigating distribution of drugs to the Fiends and the Scorpions raider gangs, posing as an associate of the drug dealer Price. He had recently had the chem dealer arrested and imprisoned, covering up the dealer's absence as a recent business opportunity that he went to check out. The Camp McCarran quartermaster Daniel Contreras soon sends the Courier to deliver a package to Price at Miguel's Pawn Shop in Westside, unaware that his contact has already been apprehended and locked up.
Dealing with Contreras: The Courier is sent to Miguel's Pawn Shop to find Price, Contreras' contact, but instead Keller is there. Talk to him and report back to Contreras. He'll ask you to kill Keller, but you can convince Contreras to work with him, Barter check of 70 or Speech check of 80. Whichever option you took go back to Keller and either kill him or convince him to work with Contreras.
pcps3xbox360 After talking with Keller, the dialogue option to pass a 7 INT/PER check pops up and does not work and always results in failure, despite having 7 Perception and 7 Intelligence.[verified]
pc After talking with Keller and passing the INT/PER check, if you choose to attack and kill Keller after he says you're under arrest, when you return to Contreras the result and dialogue option will be the same as if you kept Keller alive and bribed him to play along and keep his mouth shut about the chem trafficking. If you kill Keller in this order you will not take a hit to your reputation with the NCR, and you will gain access to the stash and This Machine. Although it disables the ability to turn him in to Lt. Boyd (This occurs as of patch #2). [verified]
ps3xbox360 Sometimes, even if you kill him without NCR reputation loss, the NCR will be hostile towards you. A fix for this is to reload to the save after you killed him but before the NCR went hostile and travel to the New Vegas Strip. [verified]
ps3 If you say that you will rat out Contreras, and then kill Keller, you will lose no reputation with the NCR. [verified]
xbox360 Upon passing the Speech check to convince Keller you are merely seeking Price to purchase from him, you will gain no XP for doing so, unlike every other Speech check in the game. [verified]