This is a bit of a tricky one to snag, and it involves some first-time “spoilers” so be forewarned if you want to avoid them. I will try and block out what I can, just in case.
For this Achievement, it’s best to do it on the first night and play a bit of a “waiting game” for the killer to arrive.
The goal is to just kind of hang around and talk with your friends until about 10:00 p.m. in-game time and then head into a closet to hide.
At around 10:45 p.m., The Killer will arrive through a secret door in the Master Bedroom.
I suggest hiding in the Master Bedroom closet and then working your way downward, listening intently for the heavy breathing of The Killer.
In one fell swoop, you need to find all the dead bodies of your friends and examine them that same evening.
Francine can usually be found in The Study Room. Occasionally, she can also be found in the Upper Hallway or the Master Bedroom itself.
From my experience, Megan will always seem to be in the living room, around the couch.
Cliff can end up in either the Kitchen, the 1st Floor Hallway, or the living room/Dining Area.
Gary seems to be all over the place! He can typically be found in the foyer, living room, or dining area. He can also appear in the upstairs hallway or Study Room.
Listen carefully for heavy, ragged breathing and the SWING of a knife to know if all four friends have perished, and carefully make your way around the home and examine each body.
NOTE: You can definitely do this on any other night in the game; however, it is, in my opinion, easiest to do this on the first night before the time loop starts in earnest. Keep in mind that the more you discover about the house, the sooner The Killer appears, especially after turning on one of the Generators.
It’s also good to note that eventually, Francine will disappear as the mystery unravels, so it’s best to try and get this Achievement in the beginning.