If you murder a guard, wait 72 hours, and then come back, all guards remember the crime. However, they are not hostile and simply say "We should throw you off the ship for what you've done, but Harkness told us forgive and forget". Harkness says similar dialogue, albeit stating that he'll "let you go just this once". However, killing the guards again and talking to Harkness will make him say that he'll let you go over and over.
If you steal a certain number of items (it doesn't seem to have to be from Rivet City), the guards will know about it, occasionally saying things like "You're a lowlife, but keep your nose clean from now on and we'll let you stay."
When a guard dies for any reason (not only if killed by the player) a new recruitment note will appear on the terminal in the bridge tower. The note will disappear after 3 days when a new guard respawns. Of course the player can't get the job and there is no additional dialogue about this.
fo3mz A Rivet City guard who had been abducted by the aliens can be found pacing around inside one of the holding cells of Mothership Zeta. If talked to, she will respond with: "This can't be happening, this can't be real!"
pcps3xbox360 Occasionally Rivet City guards can be found elsewhere in the wasteland wandering aimlessly around. The Super-Duper Mart, a common spawn point for many a non-player character, supports this spawn point for Rivet City guards for unspecified reasons. [verified]
pcps3xbox360 When you are fully hidden, and kill a Rivet City Officer when no one is around, other Security Officers will become hostile to you, until you return 24 hours later. [verified]