Hitman

Hitmen are assassins hired by Mr. Burke to kill you if you chose to save Megaton instead of blowing it up. They will have a Contract for Extermination on their person.

Conversely, if you become extremely adept at mezzing and collaring people, 4 man kill squads will come after you. They rarely pose much of a threat though, as they're armed with kitchen knives, pool cues, and at worst, switchblades. Though some have faced groups armed with laser pistols.

A Hitman squad will try to attack and kill you if you had disarmed the bomb in megaton. If you killed Mr.Burke in Megaton, the hitman squad will still attack you, and there will be a message written by the already dead Mr.Burke.