In Francis International Airport during free mode, the player can sometimes see a pedestrian walking around the runways. He looks like in-game mission boss Little Jacob, wearing his second outfit.
If the player attacks the pedestrian, with any weapon, he will not die. He will stand there for a few seconds before turning and shoot the player with a SMG until they die. The only known way to kill him is by knocking him into the water and drowning him. It has been proven that the pedestrian's spawning is a glitch, but the cause is still unknown. It is possible that there are some old, unused pedestrian paths that run through the airport, but they were not removed from the final version of the game, and the pedestrians spawn by accident in multiplayer. However, this is most likely the work of modders, where they can summon a "bodyguard" feature of invincible NPC's to shoot players. They look like Little Jacob.