When you enter Steeltown for the first time you will find a corpse in the east side of the map, past the vendor. Inspect it and take a note from it. After each step of the main steeltown questline you will find a corpse of a previously alive NPC each time near the first corpse, another three in total. There is a serial killer out there!
In order for people to die you have to take the last corpse's note and exit and re enter Steeltown Gates and also to progress/complete the steeltown questline of course. The last corpse needs a level 7 first aid skill check. After collecting all four notes, exit Steeltown and go west of it, at the area with the weird Igloo like structures. There you will find a shack. Inspect it and achievement unlocks.
It seems the serial killer might be..