Arizona Killer

Arizona Killer is a main quest in Fallout: New Vegas and an achievement/trophy for all platforms.

Synopsis
Aaron Kimball, President of the New California Republic, is making a visit to Hoover Dam to improve morale among his troops in the Mojave. His assassination would devastate NCR forces and inspire Caesar's armies.

Detailed walkthrough
After receiving instructions from Caesar (or Lucius, if Caesar is dead), the player character needs to meet Cato Hostilius, camped northwest of Ranger Station Delta. When spoken to, he will present the player character with a set of NCR armor and suggests planting a bomb on the Bear Force One (the player character can receive the Vertibird bomb from him if their Explosives skill is at least 50). Afterwards, he will make his way to Hoover Dam and blend into the crowd of spectators.

The entire area of the Dam is heavily guarded by combined patrols of NCR troopers and Rangers. The latter can see through faction disguises, the NCR will always be hostile when the disguise fails due to the failure of Don't Tread on the Bear! The player character has a limited time to make some preparations before talking to Cato again in the crowd and telling him that they are ready. Waiting for too long (well over an hour of real time), leaving the location before completing the assassination, killing any ranger atop or in the immediate area of the visitor center (even quietly, this includes the trooper Jensen) or not arriving at the dam at all will fail the quest.

Immediately after Cato is told that the player character is ready, the Bear Force One will arrive and land on top of the visitor center. President Kimball will make his way to the stage to deliver a speech. If there is any suspicion that an assassination attempt is imminent, the Rangers will interrupt and hurry the President back to the Vertibird or a secured location beneath the helipad if the aircraft is inoperable. Otherwise, after the speech ends, the President and his security detail will simply leave. The President's death completes the quest. It will fail if any of the previously mentioned criteria are met.

Note: ''Drawing a weapon while near the visitor center and after the president has arrived will result in the President and NCR reacting as if he had come under attack, even if the Courier is hidden and has not attacked. However, the NCR will not turn hostile unless they see through the Courier's disguise.''

Explosives

 * Plant a bomb on the Vertibird while it's on the helipad.
 * Cato will provide the explosive necessary to blow up the Vertibird when it takes off if the player passes an Explosives skill check of 50; it can also be pickpocketed from him. Accessing the helipad requires bypassing Jensen through stealth, persuade him with a Speech skill check of 50, or dressing as an NCR engineer (one is in the visitor center). Once planted, the bomb will explode when the Vertibird takes off.
 * Plant C-4 in Jeremy Watson's helmet.
 * Jeremy Watson is an NCR trooper who is going to be decorated by Kimball. He is missing his helmet, which is on a table next to the stairs below the visitor center. Planting C-4 in the helmet requires an Explosives skill of 50 and a brick of C-4. Watson can then be pointed towards his missing helmet. When he retrieves it, he becomes a walking bomb that can be detonated when the President turns to decorate him. You will have to wait about 2 minutes into the President's speech.

Repair

 * Rig the anti-aircraft gun to explode.
 * This is done using the console at the top of the exterior staircase (50 Repair), just east of the visitor center doors (next to a ham radio). The gun will explode just before Kimball calls up Jeremy Watson.

Science

 * Sabotage Bear Force One's flight computer.
 * This is done using the computer terminal inside the visitor center (50 Science); the Vertibird does not have to be on the helipad. When the Vertibird lands the program will be uploaded automatically; the player just has to sit back and watch as it crashes when leaving the dam.
 * Program the anti-aircraft gun to shoot down the Vertibird.
 * This is done using the console at the top of the exterior staircase (50 Science), just east of the visitor center door (next to a ham radio). The gun will spin around and take out the aircraft before it gets over the dam.
 * This is the quickest method of assassination, due to not turning the NCR hostile and the fact that Bear Force One gets shot down before it can cross over the dam. It also does not require Bear Force One to land.

Energy weapons or Guns

 * Shoot down Vertibird with personal weapons
 * The Vertibird has a high Damage Threshold and will require multiple shots from a powerful weapon such as the YCS/186 or anti-materiel rifle (even with max charge or armor piercing rounds), on all but the lowest difficulty settings.
 * Traditional sniper assassination.
 * Snipe the president using a long-range weapon. There are two notable locations: the top of the observation tower located on the rim of the Dam behind the stage (it is necessary to silently eliminate a Ranger sharpshooter on top of it first) and the base of the rocky ridge in front of the visitor center.
 * For the former option, if the player has high Sneak and a silenced long range weapon (such as a modified sniper or Varmint rifle), it is possible to kill everyone silently. It makes the getaway easier.
 * For the latter, a silenced long range weapon is recommended also. It is possible to sneak kill the president, retreat without taking a hit and quickly fast travel.
 * In either case, a sneak attack critical is required to ensure a one-shot kill, as Kimball has above average health and can withstand a non-critical headshot from most rifles.
 * For the Gun Runners' Arsenal challenge Sic Semper Tyrannis, a well-placed shot from the Hunting revolver can complete the challenge alongside the benefits of killing Kimball from a distance.
 * With a Stealth Boy, the player will be able to sneak up onto the stage behind Kimball, and with a silenced weapon can shoot him and sneak away without being detected.
 * Place C-4 near Kimball's route.
 * C-4 explosives can be placed anywhere near the President's route to and from the helipad. The best location is the middle of the helipad (which requires bypassing Jensen), where it can be detonated to kill the President and his security detail when they step out of the Vertibird.
 * Create other human bombs.
 * Requires planting several C-4 charges on Cato, Jeremy Watson, or any other NCR trooper who is close to the stage or the President's route. All of these can be later detonated simultaneously with a detonator.

Behind the scenes

 * A majority of this quest was implemented by Charles Staples.
 * The title is a reference to the song "The Arizona Killer", popularized in the 2007 film 3:10 to Yuma. The song was written by Katie Lee who adapted it from an older 1942 song "The Tennessee Killer".

Bugs

 * If the player character travels to the Fort, kills Caesar/Lucius and then returns to the Dam, President Kimball will be dead and characters neutral to the NCR will treat him as an assassin.
 * Cato can spawn very close to the cazador nest, putting him in danger of death from the moment the quest begins. To avoid this, fast-travel to the area before taking the quest, clear out all the cazadores, and then go to the Fort to receive the quest.
 * If the player character visits the Dam after receiving the quest but before making contact with Cato, the quest will automatically fail when he leaves the Dam area. If the player waits at the Dam without having met Cato, the President will never appear.
 * Sometimes the quest will fail immediately once started, forcing the player character to report failure to Caesar. This usually happens if a specific male engineer stationed at the Dam has been killed prior to starting the quest, as he is a disguised Legion soldier. The death of this engineer sets a number of variables which set the NCR trooper guarding Kimball on alert, thus automatically failing the quest once it is taken.
 * Occasionally, Kimball's Vertibird never arrives at the Dam, making this quest impossible to complete without the use of console commands. Can occur when reloading saves during the mission.