Sewer Killer is a possible myth in Grand Theft Auto Online.
Description[]
Sewer Killer is rumored to be located in the mysterious Maintenance Tunnels of Grand Theft Auto Online. He is described as wearing a filthy, stereotypical hillbilly suit, and has a mullet hairstyle, with a long mustache. The killer is said to follow the player as they progress through the darker portions of the tunnels and will immediately attempt to kill the player should they turn around while he is stalking them. Shooting the killer three times with a basic shotgun is enough to at least temporarily subdue him although the most recent report of the legendary sewer killer describes having shot him 12-13 times in total in the event the third shot did not kill him. It is unknown whether Sewer Killer stays dead for the rest of the lobby's lifespan or resuscitates after an extended period of time.
Conclusion[]
The mythical Sewer Killer is most likely just a glitched maintenance worker NPC or a player/group of players playing pranks on whoever wanders into the Maintenance Tunnels, but it is always possible that it is indeed a serial killer who stalks and eventually murders whoever enters the tunnels.