This is a simple Easter Egg, you can easily do it while you are in the mission.
● Minimap with important marks:
Minimap with important marks
● All you need to do is wait for the halftruck at the crossroads, kill the crew and take their
corpses to the rock near by.
Halftruck at the crosroads
The rock at the crossroads
● Drop the four bodies on the rock and you're done.
Corpses on the rock
● As I know, the halftruck only starts if you pass the turn after the crossroads.
● The
Easter Egg is at the end of the map, on the road which leads to the wooden house.